Tracks the maximum usage of executable memory allocated by V8 and allows the histogram data to be gathered and reported. 

This patch is contains only the usage tracking logic from 3030048 (already LGTM'd). It does not implement the RWX Limit. 

BUG=52122
TEST=Check the V8.ExecutableMemoryMax histogram in the Chrome about:histograms page

Review URL: http://codereview.chromium.org/3161015


git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5299 ce2b1a6d-e550-0410-aec6-3dcde31c8c00