Add RemoteFrameView.

Introduces RemoteFrameView, a view class for RemoteFrames within Blink.
RemoteFrameView will initially manage the WebLayer referencing the
externally rendered content, and receive notifications relating to the
frame rect being modified or resized.

BUG=346764
R=eseidel@chromium.org, dcheng@chromium.org

Review URL: https://codereview.chromium.org/214603008

git-svn-id: svn://svn.chromium.org/blink/trunk@170419 bbb929c8-8fbe-4397-9dbb-9b2b20218538