aura: Add an EasyResizeWindowTargeter.

Add EasyResizeWindowTargeter to allow easily resizing windows with mouse/touch
with the new event-dispatch code. This will eventually allow getting rid of
Window::SetHitTestBoundsOverrideOuter() once the new event-dispatch code is used
for all event types. This patch installs an EasyResizeWindowTargeter for the
shelf and status-area widgets. Subsequent CLs will install such targeters for the
toplevel windows too.

Collateral change includes adding some dependencies on wm_public (in DEPS and gyp).

BUG=318879
R=ben@chromium.org

Review URL: https://codereview.chromium.org/118553004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243177 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243177
Re-enables docked windows by default in M34 (reverts issue 109663002)

BUG=None
TEST=Visual
1. in chrome://flags verify that ash-disable-docked-windows is present.
2. in chrome://flags verify that ash-enable-docked-windows is absent.
3. When running chrome without ash-enable-docked-windows it should be possible to dock a window at a screen edge.
TEST=ash_unittests --gtest_filter=*Dock*

Review URL: https://codereview.chromium.org/123743003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243178 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243178