Add API callback for tracking allocated memory

Add API callback for tracking allocated memory

Allows the host application to provide a mechanism for notification and custom logging through a callback (set through the API V8::AddMemoryAllocationCallback and removed through V8::RemoveMemoryAllocationCallback), when V8 allocates ro frees memory.

This replaces the current histogram data "V8.ExecutableMemoryMax" by allowing usage data to be logged by the application as required rather than always through V8.

BUG=http://crbug.com/54222
TEST=Set the callback function with the API and cause V8 to allocate memory.

Patch by Paul Mehta <pmehta@chromium.org>

Review URL: http://codereview.chromium.org/3329006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5403 ce2b1a6d-e550-0410-aec6-3dcde31c8c00