Make some editing/selection functions accessible to c/b/renderer_host/

In order to have access to Cut, Copy, Paste, MoveRangeSelectionExtent,
and SelectRange functions of WebConentsImp from c/b/renderer_host/,
specifically to implement unified touch selection for Aura, these
functions are added to RenderWidgetHostDelegate interface.

BUG=399721

Review URL: https://codereview.chromium.org/1162373002

Cr-Commit-Position: refs/heads/master@{#337243}
17 files changed