[ MimeHandlerView ] Remove an unnecessary argument

The API MaybeCreateMimeHandlerView passes an int which is used as the
element instance ID for the GuestView. The int is obtained from
BrowserPluginManager::GetNextInstnaceID() which itself obtains it from
RenderThread::GenerateRoutingID() (publicly accessible to outside of
content/). This is unnecessary and can be generated inside
MimeHandlerViewFrameContainer instead.

This (mechanical) CL removes the argument from all the methods involved.

TBR=avi@chromium.org,wjmaclean@chromium.org

Bug: 659750
Change-Id: Ia20e2e2dd59f144ebaa646a4c022390398ea8e07
Reviewed-on: https://chromium-review.googlesource.com/c/1487209
Reviewed-by: Ehsan Karamad <ekaramad@chromium.org>
Reviewed-by: James MacLean <wjmaclean@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Ehsan Karamad <ekaramad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635681}
9 files changed