[ MimeHandlerView ] Navigation to PDF Resource

This CL implements the browser side hooks/logic required to support
navigation of the main frame or a subframe to a PDF resource. With the
non-frame based version the response for the navigation is intercepted,
replaced with a GUID and sent to blink where blink generates a
PluginDocument.

With frame-based MHV, a PluginDocument does not make sense (it expects
to have a PluginView inside). Instead, this CL changes the behavior such
that the response from the browser includes a templated HTML page.

The follow-up CL to this will ensure that in response to mime-types such
as PDF, blink creates a HTMLDocument instead of a PluginDocument, and
further adds the required MimeHandlerViewContainer logic to support
navigations to PDF resource.

Design Document:
https://docs.google.com/document/d/1_gJv4_fewyfjI7lcUgFX14iQxDudtEMrsjjWKpkI5BI/edit

TBR=lazyboy@chromium.org

Bug: 659750
Change-Id: Idf6bcf20450c2b50d360b8fa4033c5b9494981fd
Reviewed-on: https://chromium-review.googlesource.com/c/1460426
Reviewed-by: Ehsan Karamad <ekaramad@chromium.org>
Reviewed-by: Ɓukasz Anforowicz <lukasza@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: James MacLean <wjmaclean@chromium.org>
Commit-Queue: Ehsan Karamad <ekaramad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#633322}
9 files changed