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 &&

[vmpstr, 2014/01/10 00:52:02]

We could technically have a case where after a super quick pinch zoom, we get
that the previous high res contents scale is now a low res contents scale, which
would avoid this check but still have a low res tiling? I mean that's probably
highly unlikely...

Would setting low_res_factor to 1 in GPU raster case around line 1058 in this
file also get rid of the low res tiling?

[enne (OOO), 2014/01/10 01:42:34]

I don't think so.  I think you'd maybe need to add an additional case to
PictureLayerImpl::CleanUpTilingsOnActiveLayer to clean up low res tilings on
layers that shouldn't have low res tilings.  Or remove it here?

+      !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 270 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