GCM Registration Request
* implementation of request creation
* implementation of response parsing
* tests for both.

BUG=284553

Review URL: https://codereview.chromium.org/126513007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244561 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244561