Enable HTMLMediaElement@autoplay on Android

Enable HTMLMediaElement@autoplay on Android

This CL sets user_gesture_required_for_media_playback to false in Chrome for
Android. Previously, we removed this requirement as a special case for the
Google Search Results page. Now that this setting matches Chrome's behavior on
other platforms, we don't need the special case for google.com and can remove
the entire VoiceSearchTabHelper.

This CL leaves the user_gesture_required_for_media_playback WebPreference
because that's used by android_webview.

R=klobag@chromium.org, darin@chromium.org
BUG=178297
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=288308

[darin (slow to review), 2014-08-07 20:06:09]

LGTM

[abarth-chromium, 2014-08-08 03:43:59]

The CQ bit was checked by abarth@chromium.org

[commit-bot: I haz the power, 2014-08-08 03:45:16]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/abarth@chromium.org/447353002/20001

[commit-bot: I haz the power, 2014-08-08 10:25:56]

Change committed as 288308

[abarth-chromium, 2014-08-08 17:48:11]

A revert of this CL has been created in
https://codereview.chromium.org/453023002/ by abarth@chromium.org.

The reason for reverting is: I misunderstood the outcome of the discussion
surrounding this topic. We need to keep this code in order to not break
google.com while gathering data about this feature..