Javascript heap profiler

This profiler tracks every memory allocation and deallocation, by the
MemoryManager as well as the V4 VM, and exposes them as a stream of
events to the profiler service.

Change-Id: I85297d498f0a7eb55df5d7829c4b7307de980519
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>