[ MimeHandlerView ] Do not create PluginDocument

This CL is the second part in the implementation of navigation to PDF
resources with frame-based MimeHandlerView. This change implements the
logic for creating a MimeHandlerViewFrameContainer in response to
browser's request. To this end, when handling the resource request
response for a PDF mime-type, DOMImplementation avoids creating a
PluginDocument and implements an HTMLDocument instead. The document is
then populated with the templated HTML page injected by the plugin
response interceptor.

Design document:

Bug: 659750
Change-Id: I9a4490d99391d746333f76979e98682fa6742be7
Reviewed-on: https://chromium-review.googlesource.com/c/1477921
Reviewed-by: James MacLean <wjmaclean@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Reviewed-by: Ehsan Karamad <ekaramad@chromium.org>
Commit-Queue: Ehsan Karamad <ekaramad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634499}
6 files changed