Refactor common functionality out of webview, appview, and extensionoptions.

      This CL creates the GuestViewContainer object from which the different guestviews inherit common functionality. This allowed for a large amount of repeated code to be replaced by single copies.

BUG=431002,434226

TBR=kalman@chromium.org for extension_options.js
TBR=rockot@chromium.org for dispatcher.cc and extensions_renderer_resources.grd

Review URL: https://codereview.chromium.org/739403005

Cr-Commit-Position: refs/heads/master@{#306023}