Reducing CPU impact of non-monotonic clocks on Gc.

Adding a ceiling for the Gc's histogram's num_of_windows count, ensuring the
number of data points to insert does not become extremely large when time
changes unexpectedly. This may happen when the time source is not monotonic.

Bug: 123365804
Test: confirmed the fix behaves as intended on a system with an erratic clock
Change-Id: Idd3560204d3392fe247b65d383c41de2eaf8d35c
Signed-off-by: Vincent Palomares <paillon@google.com>