Add key based scrolling on magnified screen for kiosk mode.

* Add MagnifierKeyScroller event handler that interprets
  click and hold action.
* kAshEnableMagnifierKeyScroller to test on desktop.
* Modified EventGenerator to generate native event for key press/release.

BUG=340729
TEST=MagnifierKeyScrollerTest

Review URL: https://codereview.chromium.org/155493002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249996 0039d316-1c4b-4281-b951-d872f2087c98
[Telemetry] Add @Disabled and @Enabled decorators.

BUG=341885

Review URL: https://codereview.chromium.org/151843003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249997 0039d316-1c4b-4281-b951-d872f2087c98
Blink roll 166755:166769

http://build.chromium.org/f/chromium/perf/dashboard/ui/changelog_blink.html?url=/trunk&range=166756:166769&mode=html
TBR=
BUG=

Review URL: https://codereview.chromium.org/158413002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249998 0039d316-1c4b-4281-b951-d872f2087c98
Update .DEPS.git

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249999 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249999