Commits on Jun 22, 2022

1. [android] avoid View.Context during ContextView scrolling …

   Context: dotnet#8012
   Context: https://github.com/Kalyxt/Test_CollectionView
   
   We had some reports of poor `CollectionView` performance while
   scrolling on an older Android device.
   
   Reviewing `dotnet trace` output, I did find some issues similar to dotnet#8001:
   
       317.42ms (1.1%) mono.android!Android.Views.View.get_Context()
   
   1% of the time is spent in repeated calls to `View.Context` inside the
   `ItemContentView` class. Making a new overload for
   `ContextExtensions.FromPixel()`, I was able to remove all of these
   calls.
   
   This results in only a couple `View.Context` calls on startup now,
   much better:
   
       1.30ms (0.01%) mono.android!Android.Views.View.get_Context()
   
   Using the "janky frames" metric from the latest profiler in Android
   Studio Dolphin:
   
   https://developer.android.com/studio/profile/jank-detection
   
   With my slowest Android 12+ device, a Pixel 4a, I could actually see a
   few "janky frames" while scrolling the sample.
   
   With these changes in place, I only see 1 "janky frame" now.
   
   I also compared the before and after with the visual GPU profiler:
   
   https://developer.android.com/topic/performance/rendering/inspect-gpu-rendering
   
   It appears at a glance that these changes are better.
   
   I am unsure at what point the performance will be good enough to close
    dotnet#8012, but this helps!

   

   jonathanpeppers committed Jun 22, 2022
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