telemetry: Report ScrollingThread metrics in rendering benchmark.

Report the following UMA in rendering benchmark:
. Graphics.Smoothness.PercentDroppedFrames.ScrollingThread.TouchScroll
. Graphics.Smoothness.PercentDroppedFrames.ScrollingThread.WheelScroll

Stop reporting the following:
. Graphics.Smoothness.PercentDroppedFrames.MainThread.PinchZoom

BUG=1035460

Change-Id: Ibb959eaff8955e5ec45de4824795516c2e745163
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2098684
Commit-Queue: Caleb Rouleau <crouleau@chromium.org>
Auto-Submit: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749719}

tools/perf/benchmarks/rendering.py

@@ -29,7 +29,6 @@ RENDERING_BENCHMARK_UMA = [
     'Graphics.Smoothness.PercentDroppedFrames.AllInteractions',
     'Graphics.Smoothness.PercentDroppedFrames.AllSequences',
     'Graphics.Smoothness.PercentDroppedFrames.MainThread.MainThreadAnimation',
-    'Graphics.Smoothness.PercentDroppedFrames.MainThread.PinchZoom',
     'Graphics.Smoothness.PercentDroppedFrames.MainThread.RAF',
     'Graphics.Smoothness.PercentDroppedFrames.MainThread.TouchScroll',
     'Graphics.Smoothness.PercentDroppedFrames.MainThread.WheelScroll',
@@ -37,6 +36,8 @@ RENDERING_BENCHMARK_UMA = [
     'Graphics.Smoothness.PercentDroppedFrames.CompositorThread.PinchZoom',
     'Graphics.Smoothness.PercentDroppedFrames.CompositorThread.TouchScroll',
     'Graphics.Smoothness.PercentDroppedFrames.CompositorThread.WheelScroll',
+    'Graphics.Smoothness.PercentDroppedFrames.ScrollingThread.TouchScroll',
+    'Graphics.Smoothness.PercentDroppedFrames.ScrollingThread.WheelScroll',
     'Memory.GPU.PeakMemoryUsage.Scroll',
     'Memory.GPU.PeakMemoryUsage.PageLoad',
 ]