Add a WebContents getter callback in ResourceRequestInfo

This CL adds a method to ResourceRequestInfo that returns a callback that can
be used on the UI thread to get the WebContents associated with the request.It
is used in the SSLErrorHandler code, instead of using a RenderProcessHost ID
and a RenderFrameHost ID directly .This allows SSL error interstitials to work
with PlzNavigate enabled.

BUG = 504347

Review URL: https://codereview.chromium.org/1459473003

Cr-Commit-Position: refs/heads/master@{#361314}
20 files changed