Port r16114 (2d1bf399)

Original commit message:
This patch is to enhance the source code line information for profiler.

For the Hydrogen compilation, most of the source code line information
is not copied from the HInstruction the to corresponding LInstruction.

This patch defines one PositionBits field for LInstruction and copies the
sorce code position value from the HInstruction.

When Generating the native code, we use RecordPosition(..) function to
write LInstruction's position value to position recorder.

BUG=

Review URL: https://codereview.chromium.org/22502006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16118 ce2b1a6d-e550-0410-aec6-3dcde31c8c00