[ MimeHandlerView ] Use correct background color

When a frame is navigated to a mime-type related to MimeHandlerView, an
HTMLDocument is created by injecting an HTML string in the response. The
HTML string is in nature similar to PluginDocument, and similar to the
PluginDocument it should resepct the background color associated with
the plugin (obtained from WebPluginInfo). This CL changes the HTML
string so that it uses the correct color.

TBR=wjmaclean@chromium.org

Bug: 659750
Change-Id: Iaf3f0e3ed95cd1de2d7450cdbc6317216629f320
Reviewed-on: https://chromium-review.googlesource.com/c/1487187
Reviewed-by: Ehsan Karamad <ekaramad@chromium.org>
Reviewed-by: James MacLean <wjmaclean@chromium.org>
Commit-Queue: Ehsan Karamad <ekaramad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636038}
1 file changed