Make selection changes in a text field invalidate accessibility tree root.

Make selection changes in a text field invalidate accessibility tree root.

Since selection inside a text field is reflected in anchor/focus
attributes on the tree root, changing the selection needs to update the
cached root of the tree.

BUG=None
R=dmazzoni@chromium.org

Committed: https://crrev.com/d4d0bc6376f0d2551dc7cf4e198c81e8dba732f2
Cr-Commit-Position: refs/heads/master@{#349691}

[dmazzoni, 2015-09-17 16:36:58]

The CQ bit was checked by dmazzoni@chromium.org

[dmazzoni, 2015-09-17 16:36:58]

lgtm

https://codereview.chromium.org/1347243005/diff/1/content/renderer/accessibil...
File content/renderer/accessibility/renderer_accessibility_browsertest.cc
(right):

https://codereview.chromium.org/1347243005/diff/1/content/renderer/accessibil...
content/renderer/accessibility/renderer_accessibility_browsertest.cc:457:
WebAXObject input_obj = root_obj.childAt(0).childAt(0);
This test is unlikely to ever present a problem, but to avoid depending on the
exact location in the hierarchy, one option is WebDocument::getElementById and
then WebNode::accessibilityObject.

[commit-bot: I haz the power, 2015-09-17 16:40:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1347243005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1347243005/1

[commit-bot: I haz the power, 2015-09-17 18:26:56]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-17 18:26:57]

Try jobs failed on following builders:
  linux_android_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_android_r...)

[Peter Lundblad, 2015-09-18 14:42:21]

The CQ bit was checked by plundblad@chromium.org

[Peter Lundblad, 2015-09-18 14:42:21]

The patchset sent to the CQ was uploaded after l-g-t-m from
dmazzoni@chromium.org
Link to the patchset: https://codereview.chromium.org/1347243005/#ps40001
(title: "Disable RendererAccessibilityTest.TextSelectionShouldSendRoot for
Android; all other tests in this …")

[commit-bot: I haz the power, 2015-09-18 14:42:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1347243005/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1347243005/40001

[commit-bot: I haz the power, 2015-09-18 16:23:24]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-09-18 16:24:20]

Patchset 3 (id:??) landed as
https://crrev.com/d4d0bc6376f0d2551dc7cf4e198c81e8dba732f2
Cr-Commit-Position: refs/heads/master@{#349691}