cc: Re-use transforms from transform nodes when computing visible rects

This makes CalculateVisibleRects try to re-use the to_target and
from_target transforms stored in transform nodes whenever it needs to
compute a transform. Since these baked transforms incorporate the
target's sublayer scale, the fallback path now also includes sublayer
scale for consistency.

Testing locally on a z620, this improves property tree computation time
by 7% on Gmail, and by 20% on rAF-driven poster circle.

BUG=474725

Review URL: https://codereview.chromium.org/1060413002

Cr-Commit-Position: refs/heads/master@{#324122}

cc/trees/draw_property_utils.cc

@@ -45,12 +45,7 @@ void CalculateVisibleRects(
           target_is_root_surface ? 0 : transform_node->data.content_target_id;
       const TransformNode* target_node = transform_tree.Node(target_id);
 
-      // TODO(ajuma): Try to re-use transforms already stored in the transform
-      // tree instead of computing transforms below.
-      gfx::Transform content_to_target;
-      bool success = transform_tree.ComputeTransform(
-          transform_node->id, target_node->id, &content_to_target);
-      DCHECK(success);
+      gfx::Transform content_to_target = transform_node->data.to_target;
 
       content_to_target.Translate(layer->offset_to_transform_parent().x(),
                                   layer->offset_to_transform_parent().y());
@@ -58,8 +53,18 @@ void CalculateVisibleRects(
 
       gfx::Rect clip_rect_in_target_space;
       gfx::Transform clip_to_target;
-      success = transform_tree.ComputeTransform(
-          clip_transform_node->id, target_node->id, &clip_to_target);
+      bool success = true;
+      if (clip_transform_node->data.target_id == target_node->id) {
+        clip_to_target = clip_transform_node->data.to_target;
+      } else {
+        success = transform_tree.ComputeTransform(
+            clip_transform_node->id, target_node->id, &clip_to_target);
+        if (target_node->data.needs_sublayer_scale) {
+          clip_to_target.Scale(target_node->data.sublayer_scale.x(),
+                               target_node->data.sublayer_scale.y());
+        }
+      }
+
       if (target_node->id > clip_node->data.transform_id) {
         if (!success) {
           DCHECK(target_node->data.to_screen_is_animated);
@@ -96,8 +101,19 @@ void CalculateVisibleRects(
       gfx::Transform target_to_content;
       gfx::Transform target_to_layer;
 
-      success = transform_tree.ComputeTransform(
-          target_node->id, transform_node->id, &target_to_layer);
+      if (transform_node->data.ancestors_are_invertible) {
+        target_to_layer = transform_node->data.from_target;
+        success = true;
+      } else {
+        success = transform_tree.ComputeTransform(
+            target_node->id, transform_node->id, &target_to_layer);
+        if (target_node->data.needs_sublayer_scale) {
+          target_to_layer.matrix().postScale(
+              1.f / target_node->data.sublayer_scale.x(),
+              1.f / target_node->data.sublayer_scale.y(), 1.f);
+        }
+      }
+
       if (!success) {
         DCHECK(transform_node->data.to_screen_is_animated);