Add CHECK when removing SurfaceId from referenced_surfaces_

This surface ID should still be contained in referenced_surfaces_, but
there are crashes sometimes because the iterator from find is invalid.
Add CHECKs to see if we're attempting to remove the wrong surface id,
or if it's just not found in the structure.

Bug: 745684
Change-Id: Idf4a94f01e55ec20c51b6f72a4c7603c40226df6
Reviewed-on: https://chromium-review.googlesource.com/580404
Commit-Queue: John Bauman <jbauman@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488795}

components/viz/service/display/surface_aggregator.cc

@@ -768,7 +768,12 @@ gfx::Rect SurfaceAggregator::PrewalkTree(const SurfaceId& surface_id,
     }
   }
 
-  referenced_surfaces_.erase(referenced_surfaces_.find(surface->surface_id()));
+  // TODO(jbauman): Remove when https://crbug.com/745684 fixed.
+  CHECK(surface->surface_id() == surface_id);
+  auto it = referenced_surfaces_.find(surface_id);
+  // TODO(jbauman): Remove when https://crbug.com/745684 fixed.
+  CHECK(referenced_surfaces_.end() != it);
+  referenced_surfaces_.erase(it);
   if (!damage_rect.IsEmpty() && frame.metadata.may_contain_video)
     result->may_contain_video = true;
   return damage_rect;