Reverting this broke the flow tests for the performance overlay:
```
../../flutter/flow/layers/performance_overlay_layer_unittests.cc:70: Failure
Value of: golden_data != nullptr
Actual: false
Expected: true
```
This reverts commit 8427d73c8340c9e51492689ee66261a4a72cac9e.
* Revert "Revert "Add mock capability to PerformanceOverlayLayer (#7537)" (#7765)"
This reverts commit 693645e4645001ae460d5794fa6f5c7066677955.
* Add command line args for golden dir and font file
Behavior (visual) changes should be very minor. Things that are to be expected:
* A few things were not color managed correctly by the transform canvas (color emoji, some color filters). Those will be handled correctly with the tagged surfaces (although we're always transforming to sRGB, so nothing should change until we target a wider gamut).
* Image filtering will happen in the source color space, rather than the destination. Very minor.
* The transform canvas did caching of images in the destination color space. Now, the conversion happens at draw time. If there are performance issues, images can be pre-converted to the destination with makeColorSpace().
Building image encoding into the engine bloated the
binary size. This change will return raw bytes, and
callers who use this functionality can take on the
dependency on image encoding in their apps (via a
Dart package or a platform plugin).
Fixes https://github.com/flutter/flutter/issues/16537
