Added histograms to track fraction of heap spaces and percentage of generated crankshaft code.

Moved v8_optimized_debug default value to standalone.gypi.

Track JS allocations as they arrive with no affection on performance when tracking is switched off (Chromium issue 277984).

Performance and stability improvements on all platforms.

git-svn-id: http://v8.googlecode.com/svn/trunk@17205 ce2b1a6d-e550-0410-aec6-3dcde31c8c00