DevTools: Reveal selected placard in the callstack sidebar if needed.
DevTools: Reveal selected placard in the callstack sidebar if needed.

- The selected placard may not be visible if navigated via keyboard shortcut
- The keydown handlers should "preventDefault" to prevent scrolling
of the parent element, i.e. use "consume(true)" instead of "consume()".

R=pfeldman

Review URL: https://codereview.chromium.org/100883005

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@163965 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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