[GCM] Add proxy resolution support.

GCM will use the proxy resolver associated with the current network session
to resolve proxies. There is no direct fallback at the moment, so if a proxy
resolution completes, but doesn't handle the data properly (because it's
intercepting/mangling the response), connections will fail.

Direct fallback, and attempting alternate ports, will be introduced in a later
patch.

BUG=351889
TBR=jianli@chromium.org

Review URL: https://codereview.chromium.org/197473008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@257023 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 257023
Roll GRIT from r155 to r156

Changes:
- r156 Ignore whitelist when generating android xml.

BUG=338759

Review URL: https://codereview.chromium.org/198983003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@257024 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 257024
Refactor Chrome Now Card Dismissal Stack to use Promises

BUG=164227

Review URL: https://codereview.chromium.org/183883027

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@257025 0039d316-1c4b-4281-b951-d872f2087c98
Update .DEPS.git

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@257026 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 257026