PlzNavigate: add PDF viewer bypass hack to avoid crash.

PlzNavigate: add PDF viewer bypass hack to avoid crash.

This adds a little hack to avoid a crash in
BrowserTest.InterstitialCancelsGuestViewDialogswhen opening a PDF in Chromium
when PlzNavigate is enabled. This still doesn't make the test pass but makes it
timeout instead of crash. The final solution for this problem will come
with PlzFetch [1].

[1]: https://docs.google.com/document/d/1OpgSP0qtHzweXjTpcHTMg6n2XtB2zSg6YIqbGpmxJNY/edit?usp=sharing

BUG=504347

[carlosk, 2015-08-31 16:55:00]

carlosk@chromium.org changed reviewers:
+ clamy@chromium.org, davidben@chromium.org, fdegans@chromium.org,
nasko@chromium.org

[carlosk, 2015-08-31 16:55:00]

davidben@: PTAL.

others: FYI.

davidben@: let me know if this is what you had in mind when we talked about it
last week. I also fixed that comment you mentioned in your email that was wrong.

[davidben, 2015-09-01 18:22:56]

https://codereview.chromium.org/1323793002/diff/1/content/browser/loader/mime...
File content/browser/loader/mime_type_resource_handler.cc (right):

https://codereview.chromium.org/1323793002/diff/1/content/browser/loader/mime...
content/browser/loader/mime_type_resource_handler.cc:426: (info->IsDownload() ||
info->is_stream()))) {
I was actually thinking we should do:

if (!plz_navigate || !is_a_navigation) {
  // Current logic. Send either OnResponseStarted + OnResponseCompleted or
OnResponseStarted + OnWillRead + OnReadCompleted + OnResponseStarted depending
on payload_for_old_handler
} else {
  // Only send OnResponseCompleted with ERR_ABORTED and nothing else at all.
}

And then the entire info->IsDownload() || info->is_stream() check in
NavigationResourceHandler can go away completely. That's only needed because we
send OnResponseStarted for intercepted navigations, in turn only needed because
we send the request to DevTools that way by way of the renderer. But since we're
going to need to come up with another way to get the request to DevTools, may as
well not bother at all.

(Not sure if is_a_navigation should check for MAIN_FRAME or MAIN_FRAME +
SUB_FRAME. How does PlzNavigate on + OOPIF off behave? Does that exist?)