add leaks flag to show unref'd insts

add leaks flag to show unref'd insts

Leaks are shown optionally instead of always for tests, gm, and bench.
The current display does not show actual leaks necessarily, but
shows global objects that were not deleted when the test ended.
To enable the end-of-run leak display, pass --leaks or -l.

BUG=skia:

Committed: http://code.google.com/p/skia/source/detail?r=13151

[mtklein, 2014-01-23 15:24:15]

lgtm

https://codereview.chromium.org/143943009/diff/1/bench/benchmain.cpp
File bench/benchmain.cpp (right):

https://codereview.chromium.org/143943009/diff/1/bench/benchmain.cpp#newcode298
bench/benchmain.cpp:298: gPrintInstCount = true;
Even, gPrintInstCount = FLAGS_leaks;

[commit-bot: I haz the power, 2014-01-23 16:05:46]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/caryclark@google.com/143943009/1

[commit-bot: I haz the power, 2014-01-23 17:21:24]

Change committed as 13151