Send size to NativeViewportClient::OnCreated instead of GLES2Client::DidCreateContext

The size is not really a concept that belongs to GL. Note, we can still start creating
the context before we get OnCreated.

BUG=333157

Review URL: https://codereview.chromium.org/131153007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247496 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247496