DevTools: Optimize async call stacks: make function mirror lazily.
DevTools: Optimize async call stacks: make function mirror lazily.

Speed improvement up to 10%.

BUG=340285
R=yurys

Review URL: https://codereview.chromium.org/200333002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@169338 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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