Record allocation stack traces

This is initial implementation of allocation profiler.

Whenever new object allocation is reported to the HeapProfiler and allocation tracking is on we will capture current stack trace, add it to the collection of the allocation traces (a tree) and attribute the allocated size to the top JS function on the stack.

Format of serialized heap snapshot is extended to include information about recorded allocation stack traces.

BUG=chromium:277984
R=hpayer@chromium.org, loislo@chromium.org

Review URL: https://codereview.chromium.org/27227005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17301 ce2b1a6d-e550-0410-aec6-3dcde31c8c00