Extend TextInputClient for IMEAPI's candidatewindow* events.

To pass the state change event for candidate window to renderer,
I chose TextInputClient as an interface to notify from IME layer
to RWHV*.

This is first part of adding candidatewindow* events to Chromium,
and contains only addition of interface changes to TextInputClient.
Other implementation changes will follow.

BUG=238585
TEST=none

Review URL: https://codereview.chromium.org/80603002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237301 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237301
Reland r236746: Enable volume manager to find volume by using any paths.

The original patch is broken due to 2 reasons:

* It overrides the current directory at initialization because of unexpected
  fallback.
* Lack of null check for the return value of getVolumeInfo.

In addition, this patch removes a validation for mount paths.
This validation is useless, since it doesn't prevent any abusing, nor errors.

Previously reverted CL: crrev.com/64753005

BUG=302090, 322618
TEST=manually, browser_tests

Review URL: https://codereview.chromium.org/84653003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237302 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237302