cc: @alyssawilk @goaway

Pushing more ByteBuffers always has priority over performing the onResponseHeaders callback. You could have received the ResponseHeaders one hour ago - still no callback indicating so if you keep pushing more data.

This problem is systematic on H2 with explicit flow control when using the EM Network Thread to perform the callback logic.

There is a specific test for this in Cronet: https://source.chromium.org/chromium/chromium/src/+/main:components/cronet/android/test/javatests/src/org/chromium/net/BidirectionalStreamTest.java;l=465
This test is being ported, but is currently failing due to this issue.

And there is a PR with a simple test demonstrating the failure: #2212