Files.app: Stop to accept drag drop in the search input box.

Text input boxes accept drag drop by default. But we should prohibit to drop
files to the search input box. This CL handles dragstart and dragend events
globally and update the pointerEvents style of the input box during the drag
opration.

BUG=347452
TEST=manually

Review URL: https://codereview.chromium.org/186433004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255000 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255000
Experimental hotword-always-on feature.

This CL introduces --enable-app-list-hotword-always-on which
runs the hotword detector background and open the applist
with the voice-search UI when the hotword is detected.

This implementation is mainly for our experiment to measure
the additional power consumption. We don't expect to launch
this directly.

Note that this might be conflicted. Right now it cares like:
- 5 mins idle time disables it
- disable it if some tab is listening the audio (like google home page)

R=xiyuan@chromium.org
BUG=329160
TEST=manually

Review URL: https://codereview.chromium.org/178613005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255001 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255001