[DisplayList] DlOpReceiver testing classes should use gmock #165336

There are a number of testing classes used to test sequences of DlOpReceiver calls that all use custom code to store expected clips, or save layers, or depth indications and then explicitly implement the interface to vet those values.

These classes should probably be replaced by a global gmock version of that interface.

See these sites for potential migration:

• display_list_unittests.cc
  • SaveLayerExpector
  • SaveLayerBoundsExpector
  • DepthExpector
  • ClipExpector
• performance_overlay_layer_unittests.cc
  • ImageSizeTextBlobInspector