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 25% on rAF-driven poster circle.

BUG=474725

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

Cr-Commit-Position: refs/heads/master@{#324671}

1 files changed, 17 insertions, 0 deletions

diff --git a/cc/trees/property_tree.h b/cc/trees/property_tree.h
index f4351ba..43dcda5 100644
--- a/cc/trees/property_tree.h
+++ b/cc/trees/property_tree.h
@@ -153,6 +153,23 @@ class CC_EXPORT TransformTree final : public PropertyTree<TransformNode> {
                         int dest_id,
                         gfx::Transform* transform) const;
 
+  // Computes the change of basis transform from node |source_id| to |dest_id|,
+  // including any sublayer scale at |dest_id|.  The function returns false iff
+  // the inverse of a singular transform was used (and the result should,
+  // therefore, not be trusted).
+  bool ComputeTransformWithDestinationSublayerScale(
+      int source_id,
+      int dest_id,
+      gfx::Transform* transform) const;
+
+  // Computes the change of basis transform from node |source_id| to |dest_id|,
+  // including any sublayer scale at |source_id|.  The function returns false
+  // iff the inverse of a singular transform was used (and the result should,
+  // therefore, not be trusted).
+  bool ComputeTransformWithSourceSublayerScale(int source_id,
+                                               int dest_id,
+                                               gfx::Transform* transform) const;
+
   // Returns true iff the nodes indexed by |source_id| and |dest_id| are 2D axis
   // aligned with respect to one another.
   bool Are2DAxisAligned(int source_id, int dest_id) const;