cc: Don't perform image analysis if the DisplayItemList has no images.

cc/layers/recording_source.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layers/recording_source.h"
 
 #include <stdint.h>
 
 #include <algorithm>
 
@@ skipping 38 matching lines @@
 
   Region no_longer_exposed_region(old_recorded_viewport);
   no_longer_exposed_region.Subtract(new_recorded_viewport);
   invalidation->Union(no_longer_exposed_region);
 }
 
 void RecordingSource::FinishDisplayItemListUpdate() {
   TRACE_EVENT0("cc", "RecordingSource::FinishDisplayItemListUpdate");
   DetermineIfSolidColor();
   display_list_->EmitTraceSnapshot();
-  if (generate_discardable_images_metadata_)

[vmpstr, 2017/04/25 17:43:40]

This is the only place this flag is used afaik. If we're not relying on it then
we should remove it.

[Khushal, 2017/04/25 18:18:10]

That was my plan. After rebasing on your patch.

-    display_list_->GenerateDiscardableImagesMetadata();
 }
 
 void RecordingSource::SetNeedsDisplayRect(const gfx::Rect& layer_rect) {
   if (!layer_rect.IsEmpty()) {
     // Clamp invalidation to the layer bounds.
     invalidation_.Union(gfx::IntersectRects(layer_rect, gfx::Rect(size_)));
   }
 }
 
 bool RecordingSource::UpdateAndExpandInvalidation(
@@ skipping 83 matching lines @@
 
   TRACE_EVENT1("cc", "RecordingSource::DetermineIfSolidColor", "opcount",
                display_list_->ApproximateOpCount());
   gfx::Size layer_size = GetSize();
   skia::AnalysisCanvas canvas(layer_size.width(), layer_size.height());
   display_list_->Raster(&canvas, nullptr, gfx::Rect(layer_size), 1.f);
   is_solid_color_ = canvas.GetColorIfSolid(&solid_color_);
 }
 
 }  // namespace cc