A page created a number of ConsStrings that refer to one big string.

A page created a number of ConsStrings that refer to one big string.
Each such string requires small amount of heap memory.
Heap snapshot generator copies all the strings into internal hash map for future use.
The each copy requires much more memory than original v8 string.

I made a workaround for this. The snapshot will copy only first 1024 symbols.
A simple drive-by fix was made for a performance problem in ToCString implementation.

BUG=v8:1816
TEST=none

Review URL: http://codereview.chromium.org/8509003
Patch from Ilya Tikhonovsky <loislo@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9928 ce2b1a6d-e550-0410-aec6-3dcde31c8c00