[password autofill] Add UMA stats for password deletion.

This change also removes some unused code to delete all saved
passwords.

BUG=163247

Review URL: https://codereview.chromium.org/24653002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225447 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225447
Backend for DevTools quota managements.

Introduced handler for 'Quota.queryUsageAndQuota(securityOrigin)' command of DevTools protocol
(the command to be added in the protocol in Blink) providing detailed information about storage
usage and quota.

TBR=jochen@chromium.org for content/content_tests.gypi
BUG=281252
TEST=content_browsertests --gtest_filter=RendererOverridesHandlerTest.*

Review URL: https://codereview.chromium.org/23240002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225448 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225448