Improve showTree debug helper for ShadowRoots and focused elements
Improve showTree debug helper for ShadowRoots and focused elements

* Change ShadowRoot
  Old:  #document-fragment  0xhhhhhhhh
  New:  #shadow-root    0xhhhhhhhh

* Show 'focused' state for elements
  e.g.   DIV     0xhhhhhhhh CLASS="foo" (focused)

This CL has no changes for production.

Review URL: https://codereview.chromium.org/1648833002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#372278}

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