Click to Open PDF: Intercept navigations to PDF files in iframes.

Currently, when there are no PDF viewers available, iframes for PDF's
show up blank and immediately download the PDF. In this case, intercept
navigations to PDF files and instead open a data URL, which creates an
object element with the file. The object element shows a placeholder
with a button to view the PDF.

Bug: 737787
Change-Id: Id37e0e76c88e0046dac64baf034bbfd1d70c353d
Reviewed-on: https://chromium-review.googlesource.com/594943
Commit-Queue: Amber Won <amberwon@google.com>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Nick Carter <nick@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#495274}
7 files changed