App APIs in Pepper: C++ APIs

This CL contains supporting code for C++ APIs and the C++ equivalent of chrome.alarms.

BUG=327197
TEST=None

Review URL: https://codereview.chromium.org/116963003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243158 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243158