cc: Invalidate the full tiled layer when contents scale changes.

cc/contents_scaling_layer.cc

Index: cc/contents_scaling_layer.cc
diff --git a/cc/contents_scaling_layer.cc b/cc/contents_scaling_layer.cc
index 579af3476991b2b3fbb234bb73cef0af65f0fdd8..a9a8befec014616fe8be19a3c2da93378dd75c4f 100644
--- a/cc/contents_scaling_layer.cc
+++ b/cc/contents_scaling_layer.cc
@@ -11,7 +11,10 @@ gfx::Size ContentsScalingLayer::computeContentBoundsForScale(float scaleX, float
   return gfx::ToCeiledSize(gfx::ScaleSize(bounds(), scaleX, scaleY));
 }
 
-ContentsScalingLayer::ContentsScalingLayer() {
+ContentsScalingLayer::ContentsScalingLayer()
+    : last_update_contents_scale_x_(0.f)
+    , last_update_contents_scale_y_(0.f)
+ {
 }
 
 ContentsScalingLayer::~ContentsScalingLayer() {
@@ -35,4 +38,18 @@ void ContentsScalingLayer::didUpdateBounds() {
       contentsScaleY());
 }
 
+void ContentsScalingLayer::update(
+    ResourceUpdateQueue& queue,
+    const OcclusionTracker* occlusion,
+    RenderingStats& stats) {
+  if (drawProperties().contents_scale_x == last_update_contents_scale_x_ &&
+      drawProperties().contents_scale_y == last_update_contents_scale_y_)
+    return;
+  
+  last_update_contents_scale_x_ = drawProperties().contents_scale_x;
+  last_update_contents_scale_y_ = drawProperties().contents_scale_y;
+  // Invalidate the whole layer if scale changed.
+  setNeedsDisplayRect(gfx::Rect(bounds()));
+}
+
 }  // namespace cc