flutter/engine#51364 accidently removed the initialization of the dimensions of the skia gold client.

When the skia gold client is created now, we can see it isn't passing in the dimensions:
https://github.com/flutter/engine/pull/51364/files#diff-3293ff9aebafbda5b0a82441c8bcea256766980f79ab42cd39776cdd598bab5fR51

This is how it used to work:
https://github.com/flutter/engine/blob/2c3a86e36f6549759e409d5fd3e78f6befd48a0d/tools/golden_tests_harvester/bin/golden_tests_harvester.dart#L88

cc @matanlurey