Merging r275946 and r275948:

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r275946 | bruening | 2016-07-18 22:03:38 -0700 (Mon, 18 Jul 2016) | 5 lines

[esan] Fix sideline thread flaky assert

Fixes an esan sideline thread CHECK that failed to account for the sideline
thread reaching its code before the internal_clone() return value was
assigned in the parent.
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r275948 | bruening | 2016-07-18 22:06:48 -0700 (Mon, 18 Jul 2016) | 4 lines

[esan|wset] Fix flaky sampling tests

Adds a new esan public interface routine __esan_get_sample_count() and uses
it to ensure that tests of sampling receive the minimum number of samples.
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llvm-svn: 276114