Support for Proxies in Frame-based MimeHandlerView

The API for attaching inner and outer WebContentses only supports a
RenderFrameHost which is same-process and origin with its parent. This
is due to the fact that all GuestViews start off with a blank <iframe>
which is later swapped out with a proxy during attaching process.

For MimeHandlerViewGuest it is not guaranteed that the starting frame
in an <embed> or <object> is in 'about:blank'. This CL circumvents the
problem by first navigating a plugin frame (on the browser side) to
'about:blank' and then proceeding with the attaching process.

 Bug: 659750

Change-Id: I57d41a38e957b22c4ba3c29cb11122115373946f
Commit-Queue: Ehsan Karamad <>
Reviewed-by: Ken Buchanan <>
Reviewed-by: Alex Moshchuk <>
Reviewed-by: James MacLean <>
Cr-Commit-Position: refs/heads/master@{#599986}
13 files changed