Remove FrameInit.

This data was formerly shared between Source/core and Source/web. After
r167637 moved frame IDs into Source/core, this is write-only in
Source/web, so lifetime no longer needs to be shared. This also enables
followup patches to split shared LocalFrame/RemoteFrame functionality
out of FrameLoaderClient.

BUG=none
R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/188333002

git-svn-id: svn://svn.chromium.org/blink/trunk@168688 bbb929c8-8fbe-4397-9dbb-9b2b20218538