Change the zone allocation api.

Change the zone allocation api.

Instead of passing a size in bytes to the allocation function, we now
have a templatized Alloc function:

  zone->Alloc<Type>(len)

This is better for security, as we can check for integer overflow in
the size computation before performing the allocation.  Before, we
often failed to check this.
Committed: https://code.google.com/p/dart/source/detail?r=10254

[cshapiro, 2012-08-01 23:24:58]

lgtm

https://chromiumcodereview.appspot.com/10836061/diff/11003/runtime/vm/allocat...
File runtime/vm/allocation.cc (right):

https://chromiumcodereview.appspot.com/10836061/diff/11003/runtime/vm/allocat...
runtime/vm/allocation.cc:21: if (size > static_cast<uword>(kIntptrMax)) {
Why is this fatal?

https://chromiumcodereview.appspot.com/10836061/diff/11003/runtime/vm/allocat...
runtime/vm/allocation.cc:24: return
reinterpret_cast<void*>(isolate->current_zone()->AllocUnsafe(size));
Just curious: what is the behavior of new when there is an OOM in the native
heap?  Typically, an exception is thrown.  We have exceptions turned off, right?
 Are we guaranteed that the program will crash?  The callers do not check the
return value.

https://chromiumcodereview.appspot.com/10836061/diff/11003/runtime/vm/zone.h
File runtime/vm/zone.h (right):

https://chromiumcodereview.appspot.com/10836061/diff/11003/runtime/vm/zone.h#...
runtime/vm/zone.h:202: if (len > ((kIntptrMax - kAlignment) / element_size)) {
Why are we subtracting off the kAlignment here?  The underlying malloc may have
a different, and quite possibly larger, alignment constraint than kAlignment.