Enhance SafeStackFrameIterator to avoid triggering assertions in debug mode.
When running profiling in debug mode, several assertions in frame
iterators that are undoubtedly useful when iterator is started from a
VM thread in a known "good" state, may fail when running over a stack
of a suspended VM thread. This patch makes SafeStackFrameIterator
to proactively check addresses and bail out from iteration early,
before an assertion will be triggered.
BUG=crbug/55565
Review URL: http://codereview.chromium.org/3436006
git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5467
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