AllocationsTracker: introduce heap-profiler-always-track-allocations flag

AllocationsTracker: introduce heap-profiler-always-track-allocations flag

It gives us a chance to track allocations from start.
Also it gives us ability to create snapshot.cc with enabled allocation tracking.

BUG=none

[loislo, 2013-10-27 19:33:56]

I built v8 snapshot and ran TrackHeapAllocations with the flag and got crash.

#
# Fatal error in ../src/frames.cc, line 58
# CHECK(frame->sp() <= handler->address()) failed
#

==== C stack trace ===============================

 1: V8_Fatal
 2:
v8::internal::StackHandlerIterator::StackHandlerIterator(v8::internal::StackFrame
const*, v8::internal::StackHandler*)
 3: v8::internal::StackFrameIterator::Advance()
 4: v8::internal::JavaScriptFrameIterator::Advance()
 5:
v8::internal::JavaScriptFrameIterator::JavaScriptFrameIterator(v8::internal::Isolate*)
 6:
v8::internal::StackTraceFrameIterator::StackTraceFrameIterator(v8::internal::Isolate*)
 7: v8::internal::AllocationTracker::NewObjectEvent(unsigned char*, int)
 8: v8::internal::HeapSnapshotsCollection::NewObjectEvent(unsigned char*, int)
 9: v8::internal::HeapProfiler::NewObjectEvent(unsigned char*, int)
10:
v8::internal::HeapProfiler::RecordObjectAllocationFromMasm(v8::internal::Isolate*,
unsigned char*, int)
11: ??
Trace/breakpoint trap (core dumped)

[yurys, 2013-10-28 08:17:24]

https://codereview.chromium.org/47713002/diff/1/src/heap-profiler.h
File src/heap-profiler.h (right):

https://codereview.chromium.org/47713002/diff/1/src/heap-profiler.h#newcode88
src/heap-profiler.h:88: FLAG_heap_profiler_always_track_allocations;
Should we also call HeapProfiler::StartHeapObjectsTracking on start if the flag
is true?