cc: don't add low-res tiling to GPU rasterized layers.

cc/layers/picture_layer_impl.cc

 // Copyright 2012 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/picture_layer_impl.h"
 
 #include <algorithm>
 #include <limits>
 
 #include "base/time/time.h"
@@ skipping 927 matching lines @@
   if (!high_res) {
     high_res = AddTiling(raster_contents_scale_);
     if (raster_contents_scale_ == low_res_raster_contents_scale_)
       low_res = high_res;
   }
 
   // Only create new low res tilings when the transform is static.  This
   // prevents wastefully creating a paired low res tiling for every new high res
   // tiling during a pinch or a CSS animation.
   bool is_pinching = layer_tree_impl()->PinchGestureActive();
-  if (!is_pinching && !animating_transform_to_screen && !low_res &&
-      low_res != high_res)
+  if (ShouldHaveLowResTiling() && !is_pinching &&
+      !animating_transform_to_screen &&
+      !low_res && low_res != high_res)
     low_res = AddTiling(low_res_raster_contents_scale_);
 
   // Set low-res if we have one.
   if (!low_res)
     low_res = previous_low_res;
   if (low_res && low_res != high_res)
     low_res->set_resolution(LOW_RESOLUTION);
 
   // Make sure we always have one high-res (even if high == low).
   high_res->set_resolution(HIGH_RESOLUTION);
@@ skipping 125 matching lines @@
   std::vector<PictureLayerTiling*> to_remove;
   for (size_t i = 0; i < tilings_->num_tilings(); ++i) {
     PictureLayerTiling* tiling = tilings_->tiling_at(i);
 
     // Keep multiple high resolution tilings even if not used to help
     // activate earlier at non-ideal resolutions.
     if (tiling->contents_scale() >= min_acceptable_high_res_scale &&
         tiling->contents_scale() <= max_acceptable_high_res_scale)
       continue;
 
-    // Low resolution can't activate, so only keep one around.
-    if (tiling->resolution() == LOW_RESOLUTION)
+    // Keep low resolution tilings, if the layer should have them.
+    if (tiling->resolution() == LOW_RESOLUTION && ShouldHaveLowResTiling())
       continue;
 
     // Don't remove tilings that are being used (and thus would cause a flash.)
     if (std::find(used_tilings.begin(), used_tilings.end(), tiling) !=
         used_tilings.end())
       continue;
 
     to_remove.push_back(tiling);
   }
 
@@ skipping 123 matching lines @@
 size_t PictureLayerImpl::GPUMemoryUsageInBytes() const {
   const_cast<PictureLayerImpl*>(this)->DoPostCommitInitializationIfNeeded();
   return tilings_->GPUMemoryUsageInBytes();
 }
 
 void PictureLayerImpl::RunMicroBenchmark(MicroBenchmarkImpl* benchmark) {
   benchmark->RunOnLayer(this);
 }
 
 }  // namespace cc