Make TransformTree::CombineTransformsBetween run faster

Make TransformTree::CombineTransformsBetween run faster

TransformTree::CombineTransformsBetween is modified to compute the
combined transform between source and destination directly (without
walking the path) when the destination and all its ancestors are
flat. A unit test is added to validate the patch.

BUG=475636
TEST=passes all the unit tests along with the one added to validate the
patch. Telemetry test on poster circle page shows improvement in
performance. The draw_properties.tough_compositor:CDP_reduction percentage
improved from -287.82% to -149.36%.

Committed: https://crrev.com/fc88422b95407da518cd9bc535d50196d2d77d41
Cr-Commit-Position: refs/heads/master@{#325503}

[jaydasika, 2015-04-16 15:44:08]

jaydasika@chromium.org changed reviewers:
+ ajuma@chromium.org, vollick@chromium.org

[jaydasika, 2015-04-16 16:01:02]

The CQ bit was checked by jaydasika@chromium.org

[jaydasika, 2015-04-16 16:01:03]

The CQ bit was unchecked by jaydasika@chromium.org

[jaydasika, 2015-04-16 16:01:22]

The CQ bit was unchecked by jaydasika@chromium.org

[ajuma, 2015-04-16 17:34:37]

Nice work! I just have a few nits.

Please update the description with any statistics you have about the performance
improvement you saw when testing locally.

https://codereview.chromium.org/1096493002/diff/1/cc/trees/property_tree_unit...
File cc/trees/property_tree_unittest.cc (right):

https://codereview.chromium.org/1096493002/diff/1/cc/trees/property_tree_unit...
cc/trees/property_tree_unittest.cc:319: TEST (PropertyTreeTest,
FlattenOperationPropertyTest) {
Maybe call this something like FlatteningWhenDestinationHasOnlyFlatAncestors?

https://codereview.chromium.org/1096493002/diff/1/cc/trees/property_tree_unit...
cc/trees/property_tree_unittest.cc:322: // flatten(B*A) = flatten(B)*A
Nit: This is the property the implementation relies on, but isn't directly used
by the test itself. How about a comment along the lines of "This tests that
flattening is performed correctly when the destination and its ancestors are
flat, but the are 3d transforms and flattening between the source and
destination."?

[jaydasika, 2015-04-16 17:44:22]

https://codereview.chromium.org/1096493002/diff/1/cc/trees/property_tree_unit...
File cc/trees/property_tree_unittest.cc (right):

https://codereview.chromium.org/1096493002/diff/1/cc/trees/property_tree_unit...
cc/trees/property_tree_unittest.cc:322: // flatten(B*A) = flatten(B)*A
On 2015/04/16 17:34:37, ajuma wrote:
> Nit: This is the property the implementation relies on, but isn't directly
used
> by the test itself. How about a comment along the lines of "This tests that
> flattening is performed correctly when the destination and its ancestors are
> flat, but the are 3d transforms and flattening between the source and
> destination."?

The property is used by the test. But, I agree, the comment you suggested is
better than what's there right now, will make the change.

[ajuma, 2015-04-16 18:10:08]

lgtm with one more nit.

Also, please wait for the linux_blink_rel bot to go green before landing.

https://codereview.chromium.org/1096493002/diff/20001/cc/trees/property_tree_...
File cc/trees/property_tree_unittest.cc (right):

https://codereview.chromium.org/1096493002/diff/20001/cc/trees/property_tree_...
cc/trees/property_tree_unittest.cc:322: // and flattening between between the
source and destination.
Nit: repeated "between"

[jaydasika, 2015-04-16 18:27:31]

The CQ bit was checked by jaydasika@chromium.org

[jaydasika, 2015-04-16 18:27:32]

The patchset sent to the CQ was uploaded after l-g-t-m from ajuma@chromium.org
Link to the patchset: https://codereview.chromium.org/1096493002/#ps40001
(title: "comment in unit test modified")

[commit-bot: I haz the power, 2015-04-16 18:28:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1096493002/40001

[commit-bot: I haz the power, 2015-04-16 20:06:23]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-04-16 20:07:23]

Patchset 3 (id:??) landed as
https://crrev.com/fc88422b95407da518cd9bc535d50196d2d77d41
Cr-Commit-Position: refs/heads/master@{#325503}