cc: Make PictureLayerImpl use a better choice for animated raster scale.

cc/layers/picture_layer_impl.cc

Index: cc/layers/picture_layer_impl.cc
diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index c294a330635797c82f7186c4768a87962738ba23..01efd63f5d8d8a4d7495c3eee4990d25f1bc030d 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -1165,27 +1165,33 @@ void PictureLayerImpl::RecalculateRasterScales() {
 
   // If we're not re-rasterizing during animation, rasterize at the maximum
   // scale that will occur during the animation, if the maximum scale is
-  // known. However, to avoid excessive memory use, don't rasterize at a scale
-  // at which this layer would become larger than the viewport.
+  // known. However we want to avoid excessive memory use. If the scale is
+  // smaller than what we would choose otherwise, then it's always better off
+  // for us memory-wise. But otherwise, we don't choose a scale at which this
+  // layer's rastered content would become larger than the viewport.
   if (draw_properties().screen_space_transform_is_animating &&
       !ShouldAdjustRasterScaleDuringScaleAnimations()) {
     bool can_raster_at_maximum_scale = false;
-    if (draw_properties().maximum_animation_contents_scale > 0.f) {
-      gfx::Size bounds_at_maximum_scale = gfx::ToCeiledSize(gfx::ScaleSize(
-          bounds(), draw_properties().maximum_animation_contents_scale));
+    // TODO(ajuma): If we need to deal with scale-down animations starting right
+    // as a layer gets promoted, then we'd want to have the
+    // |starting_animation_contents_scale| passed in here as a separate draw
+    // property so we could try use that when the max is too large.
+    // See crbug.com/422341.
+    float maximum_scale = draw_properties().maximum_animation_contents_scale;
+    if (maximum_scale) {
+      gfx::Size bounds_at_maximum_scale =
+          gfx::ToCeiledSize(gfx::ScaleSize(bounds(), maximum_scale));
       if (bounds_at_maximum_scale.GetArea() <=
           layer_tree_impl()->device_viewport_size().GetArea())
         can_raster_at_maximum_scale = true;
     }
-    if (can_raster_at_maximum_scale) {
-      raster_contents_scale_ =
-          std::max(raster_contents_scale_,
-                   draw_properties().maximum_animation_contents_scale);
-    } else {
-      raster_contents_scale_ =
-          std::max(raster_contents_scale_,
-                   1.f * ideal_page_scale_ * ideal_device_scale_);
-    }
+    // Use the computed scales for the raster scale directly, do not try to use
+    // the ideal scale here. The current ideal scale may be way too large in the
+    // case of an animation with scale, and will be constantly changing.
+    if (can_raster_at_maximum_scale)
+      raster_contents_scale_ = maximum_scale;
+    else
+      raster_contents_scale_ = 1.f * ideal_page_scale_ * ideal_device_scale_;

[danakj, 2014/10/10 15:15:52]

I do find this else case a little odd, and wonder if we still need it after
this, or can remove it and just use the default scale choice ignoring the
animation if the max is too large.

   }
 
   // If this layer would create zero or one tiles at this content scale,