Add explicit monitor inflation run test.

This tests some of the same code as the monitor_pool_test
gtest. But it tests a larger pool size with the code needed to
invoke it from the Java level.  Larger pool sizes have gotten
more interesting with the new monitor pool layout.

Add a function to return the size of the current MonitorList.
Currently this is only used by this test, but it is likely to
have debugging or performance analysis uses as well.

Test: Passed on host and on angler.

Change-Id: I4f3f150044a0d8c800eb60635e074119598cfdd1