Implement Input Method related WebPlugin interface for browser plugin

This implements input method-related interfaces defined in WebPlugin
https://codereview.chromium.org/102963005
to enable minimum support of IME for brower plugin (e.g. <webview> for
Chrome apps).

BUG=235573
TEST=content_browsertests --gtest_filter=BrowserPluginHostTest.InputMethod

Review URL: https://codereview.chromium.org/103403006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240836 0039d316-1c4b-4281-b951-d872f2087c98
[rac] Parse sub-keys in validation rules of libaddressinput.

This patch parses the "sub_keys" field in the validation rules downloaded
from the server. This field will be used to identify the valid state
abbreviates in US, for example.

BUG=327046

Review URL: https://codereview.chromium.org/107863003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240837 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240836
Adds TraySessionLengthLimitTest to ash_unittests.

BUG=305812
R=bartfab@chromium.org, stevenjb@chromium.org, oshima@chromium.org
TEST=new tests

Review URL: https://codereview.chromium.org/108213009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240838 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240838