Pass FrameTreeNode (not RenderFrameHost) to NavigateToEntry.

This is primarily cleanup, since navigation is performed on frames
that can change their RenderFrameHost over time.

BUG=236848
TEST=No behavior change.

Review URL: https://codereview.chromium.org/941113002

Cr-Commit-Position: refs/heads/master@{#317217}
5 files changed