This breaks the Linux build with:
```
[ RUN ] PerformanceOverlayLayer.Gold
../../flutter/flow/layers/performance_overlay_layer_unittests.cc:70: Failure
Value of: golden_data != nullptr
Actual: false
Expected: true
Golden file not found: "/b/s/w/ir/k/src/flutter/testing/resources"/performance_overlay_gold.png.
Please either set --golden-dir, or make sure that the unit test is run from the right directory (e.g., flutter/engine/src).
```
This reverts commit 3f0ce769e2.
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 8427d73c83.
* Revert "Revert "Add mock capability to PerformanceOverlayLayer (#7537)" (#7765)"
This reverts commit 693645e464.
* Add command line args for golden dir and font file