DevTools: fix flickering, unwanted node highlight in Elements

Panel switching and page reloading could trigger re-focusing the
ElementsTreeOutline, producing unwanted node overlays.

In this CL
- Trees highlight nodes when selection changes (pre-Nov behavior),
  instead of highlight on focusin
- Hide node highlight when focus moves to non-highlightable elements
- Console will use a custom method to select and ensure the node is
  highlighted

Bug: 913084
Change-Id: I8b56b77c0aa8c34f5f7a819434510d549b139650
Reviewed-on: https://chromium-review.googlesource.com/c/1368770
Reviewed-by: Joel Einbinder <einbinder@chromium.org>
Commit-Queue: Erik Luo <luoe@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616197}
6 files changed