Adds PerContextData::context_holder()

I need this as WebKit creates the ContextHolder and I need a handle to
it.

BUG=none
TEST=none
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/184013002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254250 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254250
options: handle "Show advanced settings..." clicks while advanced settings are hiding.

R=ajuma@chromium.org
BUG=346611

Review URL: https://codereview.chromium.org/184193002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254251 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254251