Fill in one-word-fillers for the unused property fields (Chromium issue 240056).

Removed use_system_v8 logic from the mainline gyp file (Chromium issue 226860).

Skip CPU profiler samples where top function's stack frame is not set up properly (issue 2628).

Performance and stability improvements on all platforms.

git-svn-id: http://v8.googlecode.com/svn/trunk@14720 ce2b1a6d-e550-0410-aec6-3dcde31c8c00