Remove RenderFrameHost pointer from ChooserController.

This change removes the raw RenderFrameHost pointer from
ChooserController and instead either computes necessary values (such as
the title) at construction time or stores a weak pointer to the object
derived from the RenderFrameHost.

BUG=697486

Review-Url: https://codereview.chromium.org/2746313002
Cr-Commit-Position: refs/heads/master@{#456876}
16 files changed