Recurse WebContentsTree when registering FrameSinkIDs.

When attaching WebContents into the WebContentsTree, the inner
WebContents may have child nodes. If so, they will have registered
their FrameSinkIDs with the inner WebContent's InputEventRouter.
and will not received events that are routed by the outer
WebContents' (or higher) InputEventRouter.

In this CL, we make sure that not only does the inner WebContents
register its FrameSinkID (thus attaching to the appropriate
InputEventRouter), but all the child WebContents do so as well.

Bug: 768526
Change-Id: Ib1aaf9f04beee1f53c78aa04f6abfaa98c4bfa0f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1498458
Commit-Queue: James MacLean <wjmaclean@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638109}
6 files changed