cc: Only create tilings for layers that draws content.

cc/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/picture_layer_impl.h"
 
 #include "base/time.h"
 #include "cc/append_quads_data.h"
 #include "cc/checkerboard_draw_quad.h"
 #include "cc/debug_border_draw_quad.h"
@@ skipping 110 matching lines @@
                  outside_bottom_edge && useAA);
     quadSink.append(quad.PassAs<DrawQuad>(), appendQuadsData);
   }
 }
 
 void PictureLayerImpl::dumpLayerProperties(std::string*, int indent) const {
   // TODO(enne): implement me
 }
 
 void PictureLayerImpl::didUpdateTransforms() {
-  tilings_.SetLayerBounds(bounds());
-  // TODO(enne): Add more tilings during pinch zoom.
-  if (!tilings_.num_tilings()) {
-    gfx::Size tile_size = layerTreeHostImpl()->settings().defaultTileSize;
-    tilings_.AddTiling(contentsScaleX(), tile_size);
-    // TODO(enne): handle invalidations, create new tiles
+  if (drawsContent()) {
+    tilings_.SetLayerBounds(bounds());
+    // TODO(enne): Add more tilings during pinch zoom.
+    if (!tilings_.num_tilings()) {
+      gfx::Size tile_size = layerTreeHostImpl()->settings().defaultTileSize;
+      tilings_.AddTiling(contentsScaleX(), tile_size);
+      // TODO(enne): handle invalidations, create new tiles
+    }
+  } else {
+    tilings_.Reset();
   }
 
   gfx::Transform  current_screen_space_transform = screenSpaceTransform();
   double current_time =
       (base::TimeTicks::Now() - base::TimeTicks()).InSecondsF();
   double time_delta = 0;
   if (last_update_time_ != 0 && last_bounds_ == bounds() &&
       last_content_bounds_ == contentBounds() &&
       last_content_scale_x_ == contentsScaleX() &&
       last_content_scale_y_ == contentsScaleY()) {
@@ skipping 25 matching lines @@
       GL_RGBA,
       rect,
       tiling->contents_scale()));
 }
 
 void PictureLayerImpl::SyncFromActiveLayer(const PictureLayerImpl* other) {
   tilings_.CloneFrom(other->tilings_);
 }
 
 }  // namespace cc