Shortcuts e and c select (and make visible) the next effect/control
node downwards in the chain; ALT+e/c moves upward.

Additionally, the graph bounding box is redetermined every time the
graph is redrawn (instead of only when relayouted).

Bug: v8:7327
Change-Id: If01b16fc25273703e25e429bdc36753a2fa87f7c
Reviewed-on: https://chromium-review.googlesource.com/1064210
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53259}