Avoid any race conditions with RenderFrame getting notified that it's prerendering.

Originally PrerenderHelper was per RenderView. In r239860 I switched it to be per RenderFrame. Before PrerenderHelper was guaranteed to get the IPC telling it that it's prerendering before any navigation. After the change, the RenderFrame could be navigated by its parent frame before it gets the IPC that it's prerendering. This change ensures that there are no races by having a child frame check with its parent frame if it's pre-rendering at construction.

We haven't yet turned on RenderFrame per frame, but this is something could happen once we do.

BUG=304341
R=tburkard@chromium.org

Review URL: https://codereview.chromium.org/120263006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243093 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243093
Remove calls of PrerenderTracker::TryCancel on UI thread and instead have them call PrerenderContents::Destroy directly.

This is part of the work on removing calls to ResourceRequestInfo::GetAssociatedRenderView. The last callers to that method are using it to cancel prerenders if they haven't been used yet, so the checking/cancelling needs to all move to the UI thread.

BUG=304341
R=tburkard@chromium.org

Review URL: https://codereview.chromium.org/109983006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243094 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243094