GitLab

For RenderWidgetHostImpl created on behalf of the browser process,
replace raw pointers by std::unique_ptr.

Currently, the owners of the RenderWidgetHostImpl are:
 1. The RenderViewHostImpl. In this case the main RenderFrameHostImpl
    "borrows" the RenderWidgetHostImpl from it.
 2. The local-root RenderFrameHostImpl.

For RenderWidgetHostImpl created on behalf of the renderer process, they
continue to use raw pointers and to self-destroy via IPC.

Bug: 545684, 950969
Change-Id: If08e8634d7b329cae42b2101307a54750bfb61f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1559186Reviewed-by: danakj <danakj@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Reviewed-by: Charlie Reis <creis@chromium.org>
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659022}