Reset growth control state after isolate initialization.

Reset growth control state after isolate initialization.

(a) When enabling the growth control, e.g. after isolate
initialization, the current usage should be the new basis for
growth control. This is consistent with the behavior before
r34747.

(b) Advise GC only when the number of allowed pages has been
(strictly) exceeded, rather than met. This is consistent with
the behavior before r34747.

Part (a) fixes the Havlak performance regression (3%).

R=iposva@google.com

Committed: https://code.google.com/p/dart/source/detail?r=34793

[Ivan Posva, 2014-04-07 18:38:05]

LGTM -ip

[koda, 2014-04-07 18:40:47]

Committed patchset #2 manually as r34793 (presubmit successful).