Merge to m57: Improve live region performance

Merge to m57: Improve live region performance

Previously, we explicitly omitted alert nodes from being processed as live regions to address hangs in ChromeVox.

- before this patch, ChromeVox would generate output for the same live region potentially the same number of times we get a tree change under the live region container; this could be thousands of times
- we walked up the ancestry chain using a recursive call
- we walked up the final container node's ancestry chain looking for a previously outputted live region

Fixes:
- walk up ancestry chain looking for the live region container first
- move logic to check if the live region container was previously processed immediately after (without any tree walking since the map could only contain live region containers)

TEST=manual on Gmail's keyboard shortcuts page (?). Delete a message with '#'. Verify appropriate alert output.
BUG=681417
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation
TBR=dtseng@chromium.org

Review-Url: https://codereview.chromium.org/2640283004
Cr-Commit-Position: refs/heads/master@{#445469}
(cherry picked from commit 82e8eb7b5935197660fe3ef05c8ef05e9e5d8c26)

Review-Url: https://codereview.chromium.org/2653803002 .
Cr-Commit-Position: refs/branch-heads/2987@{#46}
Cr-Branched-From: ad51088c0e8776e8dcd963dbe752c4035ba6dab6-refs/heads/master@{#444943}
Committed: https://chromium.googlesource.com/chromium/src/+/9165ea416a31dce68c0409e34022d51a871c3133

[David Tseng, 2017-01-23 23:41:45]

Description was changed from

==========
Merge to m57: Improve live region performance

Previously, we explicitly omitted alert nodes from being processed as live
regions to address hangs in ChromeVox.

- before this patch, ChromeVox would generate output for the same live region
potentially the same number of times we get a tree change under the live region
container; this could be thousands of times
- we walked up the ancestry chain using a recursive call
- we walked up the final container node's ancestry chain looking for a
previously outputted live region

Fixes:
- walk up ancestry chain looking for the live region container first
- move logic to check if the live region container was previously processed
immediately after (without any tree walking since the map could only contain
live region containers)

TEST=manual on Gmail's keyboard shortcuts page (?). Delete a message with '#'.
Verify appropriate alert output.
BUG=681417
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation
TBR=dtseng@chromium.org

Review-Url: https://codereview.chromium.org/2640283004
Cr-Commit-Position: refs/heads/master@{#445469}
(cherry picked from commit 82e8eb7b5935197660fe3ef05c8ef05e9e5d8c26)
==========

to

==========
Merge to m57: Improve live region performance

Previously, we explicitly omitted alert nodes from being processed as live
regions to address hangs in ChromeVox.

- before this patch, ChromeVox would generate output for the same live region
potentially the same number of times we get a tree change under the live region
container; this could be thousands of times
- we walked up the ancestry chain using a recursive call
- we walked up the final container node's ancestry chain looking for a
previously outputted live region

Fixes:
- walk up ancestry chain looking for the live region container first
- move logic to check if the live region container was previously processed
immediately after (without any tree walking since the map could only contain
live region containers)

TEST=manual on Gmail's keyboard shortcuts page (?). Delete a message with '#'.
Verify appropriate alert output.
BUG=681417
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation
TBR=dtseng@chromium.org

Review-Url: https://codereview.chromium.org/2640283004
Cr-Commit-Position: refs/heads/master@{#445469}
(cherry picked from commit 82e8eb7b5935197660fe3ef05c8ef05e9e5d8c26)

Review-Url: https://codereview.chromium.org/2653803002 .
Cr-Commit-Position: refs/branch-heads/2987@{#46}
Cr-Branched-From:
ad51088c0e8776e8dcd963dbe752c4035ba6dab6-refs/heads/master@{#444943}
Committed:
https://chromium.googlesource.com/chromium/src/+/9165ea416a31dce68c0409e34022...
==========

[David Tseng, 2017-01-23 23:41:46]

Committed patchset #1 (id:1) manually as
9165ea416a31dce68c0409e34022d51a871c3133 (presubmit successful).