Use profile summary to disable peeling for huge working sets

Summary:
Detect when the working set size of a profiled application is huge,
by comparing the number of counts required to reach the hot percentile
in the profile summary to a large threshold*.

When the working set size is determined to be huge, disable peeling
to avoid bloating the working set further.

*Note that the selected threshold (15K) is significantly larger than the
largest working set value in SPEC cpu2006 (which is gcc at around 11K).

Reviewers: davidxl

Subscribers: mehdi_amini, mzolotukhin, eraman, llvm-commits

Differential Revision: https://reviews.llvm.org/D36288

llvm-svn: 310005