cc: Remove fixed raster scale, stop rasterizing with will-change.

cc/layers/picture_layer_impl_unittest.cc

Index: cc/layers/picture_layer_impl_unittest.cc
diff --git a/cc/layers/picture_layer_impl_unittest.cc b/cc/layers/picture_layer_impl_unittest.cc
index 61ac6bb99b8dd4d47431757071940e6e5532e8dc..399639bda894334a432038bc39c3cd9405a47979 100644
--- a/cc/layers/picture_layer_impl_unittest.cc
+++ b/cc/layers/picture_layer_impl_unittest.cc
@@ -925,6 +925,7 @@ TEST_F(PictureLayerImplTest, CleanUpTilings) {
   float page_scale = 1.f;
 
   SetupDefaultTrees(layer_bounds);
+  active_layer()->SetHasWillChangeTransformHint(true);

[danakj, 2016/06/16 18:15:29]

What do you think of the test changes in
https://codereview.chromium.org/1474853002/diff/1/cc/layers/picture_layer_imp...
vs the changes you made here to use will-change?

   EXPECT_EQ(2u, active_layer()->tilings()->num_tilings());
   EXPECT_EQ(1.f, active_layer()->HighResTiling()->contents_scale());
 
@@ -1829,6 +1830,7 @@ TEST_F(PictureLayerImplTest,
   SetInitialDeviceScaleFactor(2.f);
 
   SetupDefaultTreesWithFixedTileSize(layer_bounds, tile_size, Region());
+  active_layer()->SetHasWillChangeTransformHint(true);
 
   // One ideal tile exists, this will get used when drawing.
   std::vector<Tile*> ideal_tiles;
@@ -3119,22 +3121,53 @@ TEST_F(PictureLayerImplTest, RasterScaleChangeWithoutAnimation) {
   EXPECT_BOTH_EQ(HighResTiling()->contents_scale(), 2.f);
 
   // Changing the source scale without being in an animation will cause
-  // the layer to reset its source scale to 1.f.
+  // the layer to change scale.
   contents_scale = 3.f;
 
   SetContentsScaleOnBothLayers(contents_scale, device_scale, page_scale,
                                maximum_animation_scale,
                                starting_animation_scale, animating_transform);
-  EXPECT_BOTH_EQ(HighResTiling()->contents_scale(), 1.f);
+  EXPECT_BOTH_EQ(HighResTiling()->contents_scale(), 3.f);
+
+  contents_scale = 0.5f;
+
+  SetContentsScaleOnBothLayers(contents_scale, device_scale, page_scale,
+                               maximum_animation_scale,
+                               starting_animation_scale, animating_transform);
+  EXPECT_BOTH_EQ(HighResTiling()->contents_scale(), 0.5f);
+
+  // However, if the layer has a will-change property, then the raster scale
+  // will get fixed at the last value.
+  active_layer()->SetHasWillChangeTransformHint(true);
+  pending_layer()->SetHasWillChangeTransformHint(true);
+
+  contents_scale = 3.f;
+
+  SetContentsScaleOnBothLayers(contents_scale, device_scale, page_scale,
+                               maximum_animation_scale,
+                               starting_animation_scale, animating_transform);
+  EXPECT_BOTH_EQ(HighResTiling()->contents_scale(), 0.5f);
 
   // Further changes to the source scale will no longer be reflected in the
   // contents scale.
-  contents_scale = 0.5f;
+  contents_scale = 1.f;
 
   SetContentsScaleOnBothLayers(contents_scale, device_scale, page_scale,
                                maximum_animation_scale,
                                starting_animation_scale, animating_transform);
-  EXPECT_BOTH_EQ(HighResTiling()->contents_scale(), 1.f);
+  EXPECT_BOTH_EQ(HighResTiling()->contents_scale(), 0.5f);
+
+  // Disabling the will-change hint will once again make the raster scale update
+  // with the ideal scale.
+  active_layer()->SetHasWillChangeTransformHint(false);
+  pending_layer()->SetHasWillChangeTransformHint(false);
+
+  contents_scale = 3.f;
+
+  SetContentsScaleOnBothLayers(contents_scale, device_scale, page_scale,
+                               maximum_animation_scale,
+                               starting_animation_scale, animating_transform);
+  EXPECT_BOTH_EQ(HighResTiling()->contents_scale(), 3.f);
 }
 
 TEST_F(PictureLayerImplTest, LowResReadyToDrawNotEnoughToActivate) {
@@ -3385,6 +3418,7 @@ TEST_F(NoLowResPictureLayerImplTest, CleanUpTilings) {
   float page_scale = 3.2f;
   float scale = 1.f;
 
+  active_layer()->SetHasWillChangeTransformHint(true);
   ResetTilingsAndRasterScales();
 
   SetContentsScaleOnBothLayers(scale, device_scale, page_scale, 1.f, 0.f,