[Google] Refine hot caller heuristic

[Easwaran Raman]

The current hot caller heuristic simply promotes edges whose caller is
hot. This patch does the following:
* Turn it off for applications with large footprint since the size
increase hurts them
* Be more selective by considering arguments to callee when the
heuristic is enabled.

This performs well on internal benchmarks. Ok for google/4_8 branch if
all tests pass?

- Easwaran
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