Remove GlobalHandles::number_of_weak_handles_ and number_of_global_object_weak_handles_

Remove GlobalHandles::number_of_weak_handles_ and number_of_global_object_weak_handles_

This is a preparation patch for inlining MakeWeak() and Clear().

Given that NumberOfWeakHandles() is used only by CHECK_EQ() in serialized.cc and that NumberOfGlobalObjectWeakHandles is unused, it is wasteful to keep track of number_of_weak_handles_ and number_of_global_object_weak_handles_ at every MakeWeak() and Clear(). Instead, we can count the number at the point where NumberOfWeakHandles() or NumberOfGlobalObjectWeakHandles() is called.

BUG=

Review URL: https://codereview.chromium.org/11958015
Patch from Kentaro Hara <haraken@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13443 ce2b1a6d-e550-0410-aec6-3dcde31c8c00