Fix several inconsistencies in the Android accessibility node tree.

Issues addressed:
- Root of the virtual hierarchy being a different node (as in Object.equals)
  than the parent's child at this location.
- The root of th evirtual node tree reporting no parent.
- Accessibility changing without an event being sent to the Android framework.
- WINDOW_CONTENT_CHANGED events being sent on non-existent nodes.

BUG=327075
R=dmazzoni@chromium.org

Review URL: https://codereview.chromium.org/110783002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240481 0039d316-1c4b-4281-b951-d872f2087c98
Rename CurrentBrowserContext to ActiveBrowserContext
Remove use of GetDefaultProfileXXX in
- c/b/ui/ash/chrome_shell_delegate*
- c/b/ui/ash/keyboard_controller_proxy.cc
- c/b/ui/ash/screenshot_taker.cc

BUG=322682

Review URL: https://codereview.chromium.org/112153002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240482 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240482
Move NativeAppWindowViews constructor to Init() so it can call polymorphic methods on itself.

BUG=327565
TBR=benwells@chromium.org

Review URL: https://codereview.chromium.org/112493002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240483 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240483