Implements a new API to set a function entry hook for profiling.

Implements a new API to set a function entry hook for profiling.

Exposes a new API; V8::SetFunctionEntryHook.
If a non-NULL function entry hook is set, the code generator(s) will invoke on the entry hook at the very start of each generated function.

Committed: https://code.google.com/p/v8/source/detail?r=12069

Review URL: https://chromiumcodereview.appspot.com/10706002
Patch from Sigurður Ásgeirsson <siggi@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12083 ce2b1a6d-e550-0410-aec6-3dcde31c8c00