Travis builds have become slow during busy periods of the day due to various reasons. This PR does the following:

Reorganizes build tasks across fewer build shards
Reduces the number of VMs used by PR and master builds to 2
No longer does a full gulp dist for unit tests (Possible to do after #9404)
Reduces the total CPU time used for PR builds to < 20 mins
Fixes #9500
Fixes #9387

* Animations: full on-action API

* review fixes

* Amp-imgur : Implement imgur embed (#9405)

* amp-imgur test code modified

* amp-imgur validation code changed

* fix amp-imgur lint check

* Remove unused Layour variables

* Test code modified

* Ingegration amp-imgur extension

* [amp-imgur] add resize logic

* Remove 3p iframes and add resize message listener

* Fix some code with reviews
* change some syntax
* change validation rules
* add find event source

* [amp-imgur] remove unnecessary code and add object check

* remove spec_name from validation code

* Remove unnecessary code and add owners file

* Change required tag name  to  in validation file

* data-imgurid -> data-imgur-id

* Add whitelist for amp-imgur

* remove unused AmpImgur import in test file

* remove unused preconnect callback

Added updates and corrections per Dima's feedback.

* Animations: support style keyframes

* docs

* review fixes

* lints

* Animations: subtargets format

* fix docs

* Add callouts for CORS + cleanup

* Update amp-access.md

…9613)

* Send default safeframe version on ad request

* fix test failure

…9617)

* Added doubleclick specific config

* Modified other networks

* Update MockA4AImpl

* Remove unneeded config lines

* Add cid, remove renderStartImplemented

* Fix lint complaint

* Changed from mandatory config to overrrideable method

* Addressed feedback, modified getAdCid

* Addressed additional feedback

* Responded to feedback

* Removed unnneeded guard against null value

* Changed signature of function

* Fixed lint issues

* addressed comments

* Addressed comments, fixed broken test

* Change signature / update tests

* more bind test fixes

* include object.assign polyfill

* move polyfills to separate file

* replace use of map() from bind-validator with ownProperty()

* fix types and test

…Only for the NON SNAP-POINTS flow) (#9668)

* removing overflow touch on no-scroll for ios

* Stop using IOS elastic scroll when slidescroll takes over animation (Only for the NON SNAP-POINTS flow)

* A4A: expose visibilityCsi

* tests

* move element service changes from #9447

* store element service ids in extension struct

* add unit test, fix other tests

* Write cookie for ad-cid.

* fix tests

* Add support for LaterPay subscriptions

* Fix canonical link on laterpay example

* Tweak default styling

* Add an example locale message for the header

* Change image to static link hosted on ampproject.org

* Update amp-iframe doc w example + gen cleanup

* Added experiment branches corresponding to exp=a4a:(5|6).

* Removed test file.

* Removed changes to yarn.lock + minor fixes.

* Fixed adsense-a4a-config.js.

* Fixed return statement.

As style tag for `opacity` was replaced with `amp-boilerplate (back in this [commit](0a056ca), updated the text to reflect those changes.

* split bind fixtures into one file per extension

* fix width/height binding bug, avoid race condition w/ dynamic containers

* actually, just skip the tests affected by race condition for now

* Remove timer calls to prevent future flakiness

* Revert the line order change

* Poll instead of using stub callback constructor

* Add jsdoc and rename variables

)

* Load examiner.js when #development=1

* address comments

* Use development=2

* Fix presubmit

* Implementation of the amp-ad-exit component for managing ad navigation (#8515).

Changes from the I2I:
- Only RANDOM, CLICK_X, and CLICK_Y variables can be used, alongside custom vars.
- It doesn't work well with <a> tags - the tap action doesn't trigger on middle clicks. Recommendation is to use other elements.
- ClickLocationFilter for border click protection is not yet implemented. It will be added in a future change.

The component does some lightweight validation of the JSON config when it's
built. This may be overkill.

Tested:
gulp test --files 'extensions/amp-ad-exit/0.1/test/*'
gulp check-types

* Update JSDoc for some functions. Fix lint issue (ignore unused parameters in an interface method).

* sinon.spy -> sandbox.spy

* Add amp-ad-exit to the list of allowed extensions in A4A pages and fix validation rules.

Address PR: add experiment flag; use camelCase for config properties

address some comments

Instantiate a new Filter for each spec.

* Instantiate a new Filter for each spec.

* remove duplicate doctype tag in example

* Make ActionEventDef public for type annotations.

* Add filter factory.

* fix event var

* update type annotation for Filter.filter

* address PR comments

* Move filter config validation to the ctor. Remove Filter.buildCallback().

* camelCase in documentation examples

* Introduce yield.

* Address comments.

* fix done state error handling

`amp-access` is a special target that's not mentioned in this document.
It's special because you can't give an arbitrary ID to it, i.e., you
can't just change the id of the `amp-access` script tag to `amp-access2`
and expect `on="tap:amp-access2.login"` to work. Given that the
"actions" for `amp-access` is a bit dynamic depending on the structure
of the `amp-access` JSON, instead of listing out the actions in a
tabular form, a reference to the `amp-access` documentation is added.

This reverts commit 98ecb9b.

It turns out that while using Docker containers instead of VMs on Travis reduces VM startup time, it has significantly increased build and test time, increasing the overall PR check round trip from < 20 mins to > 30 mins.

Compare https://travis-ci.org/ampproject/amphtml/jobs/238464404 (Docker) against https://travis-ci.org/ampproject/amphtml/jobs/238462066 (VM).

Fixes #9651

* Add validator tests for amp-imgur.

* Disallow amp-embed as child of amp-app-banner.

* Minor cleanup, Make sure our set numbers are consistent in javascript.

* adapt code from #8897

* also_requires_attr should be in trigger

* Minor cleanup of amp-ad-exit

* Disallow amp-ad/amp-embed as children of amp ad containers when data-multi-size is present.

* Revision bump

* Enabling queryparam addition to anchour links

* Code review changes

Prior to this PR, gulp build --css-only would take ~ 1 minute to run, and end up building a bunch of js files in addition to compiling css.

After this PR, gulp build --css-only takes ~ 0.5 seconds to run (a 100x speed up), and the only output files in build/ after running it are .css, and .css.js files.

Resulting speeds on my workstation:
gulp build --css-only: ~500ms
gulp build: ~1m 45s
gulp dist --fortesting: ~3m 30s

Fixes #9640

* add amp-analytics Facebook Pixel support

* add amp-analytics Facebook Pixel support

* fix test on extensions/amp-analytics/0.1/test/vendor-requests.json

* add Facebook Pixel standard events https://developers.facebook.com/docs/ads-for-websites/pixel-events/v2.9#events

* Update vendors.js

fix conflicts

* Update vendors.js

fix conflicts

* Update vendor-requests.json

fix conflicts

* Update vendor-requests.json

fix conflicts

* Update vendor-requests.json

* Update analytics.amp.html

* Update analytics-vendors.amp.html

* Update vendors.js

* Update analytics-vendors.amp.html

* fix lint error

* update

* facebook pixel

* Update vendor-requests.json

* Update analytics.amp.html

* fix lint error

* fix lint error

*  fix alphabetical order

* Update yarn.lock

* AMP-ad supports Seznam Imedia ad network

* Fixed requested changes

* Fixed requested changes

* Render API implemented

* Improved placing ads

* Fixed requested changes

* Render API fixed context
* Renamed IM.cz to Imedia
* Described JSON parameters