cc: Remove unused ImageInvalidationUpdateDuration histogram.

This was originally added to understand whether an increase in pending
tree duration for the CompositorImageAnimation experiment was resulting
from time spent in these impl-side invalidations.

Its clear that this is not the case. On Android stable, this value is
~0.45 ms at the 99th percentile. We don't need continuous monitoring
of this metric, marking it obsolete.

R=enne@chromium.org

Bug: 826115
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I44b4346c1466d5d29fd534dfc2879ed14a740169
Reviewed-on: https://chromium-review.googlesource.com/985100Reviewed-by: enne <enne@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549389}

cc/trees/layer_tree_host_impl.cc

@@ -175,9 +175,6 @@ DEFINE_SCOPED_UMA_HISTOGRAM_TIMER(PendingTreeDurationHistogramTimer,
                                   "Scheduling.%s.PendingTreeDuration");
 DEFINE_SCOPED_UMA_HISTOGRAM_TIMER(PendingTreeRasterDurationHistogramTimer,
                                   "Scheduling.%s.PendingTreeRasterDuration");
-DEFINE_SCOPED_UMA_HISTOGRAM_TIMER(
-    ImageInvalidationUpdateDurationHistogramTimer,
-    "Scheduling.%s.ImageInvalidationUpdateDuration");
 
 LayerTreeHostImpl::FrameData::FrameData() = default;
 LayerTreeHostImpl::FrameData::~FrameData() = default;
@@ -415,8 +412,6 @@ void LayerTreeHostImpl::UpdateSyncTreeAfterCommitOrImplSideInvalidation() {
   // Defer invalidating images until UpdateDrawProperties is performed since
   // that updates whether an image should be animated based on its visibility
   // and the updated data for the image from the main frame.
-  {
-    ImageInvalidationUpdateDurationHistogramTimer image_invalidation_timer;
     PaintImageIdFlatSet images_to_invalidate =
         tile_manager_.TakeImagesToInvalidateOnSyncTree();
     if (ukm_manager_)
@@ -427,7 +422,6 @@ void LayerTreeHostImpl::UpdateSyncTreeAfterCommitOrImplSideInvalidation() {
             CurrentBeginFrameArgs().frame_time);
     images_to_invalidate.insert(animated_images.begin(), animated_images.end());
     sync_tree()->InvalidateRegionForImages(images_to_invalidate);
-  }
 
   // Note that it is important to push the state for checkerboarded and animated
   // images prior to PrepareTiles here when committing to the active tree. This

tools/metrics/histograms/histograms.xml

@@ -79796,6 +79796,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 
 <histogram name="Scheduling.ImageInvalidationUpdateDuration"
     units="microseconds">
+  <obsolete>
+    Deprecated 03/28/2018
+  </obsolete>
   <owner>khushalsagar@chromium.org</owner>
   <summary>
     Duration for updating animated images and invalidating layers for images