Reviewed by Darin.

    Reviewed by Darin.

	<rdar://problem/3794735> Gmail- sending a very long message with Safari is so slow it seems like a hang

	* kjs/string_object.cpp:
        (StringProtoFuncImp::call): Replaced implementation of replace()
	method with function below...
	(replace): In order to avoid excessive allocation and copying,
	figure out the ranges of the original string and replacement
	strings to be assembled, instead of constantly creating new
	strings at each substitution. The old behavior is basically O(N^2)
	for a global replace on a pattern that matches many places in the
	string.
        (regExpIsGlobal): Helper function for the above.
        (expandSourceRanges): ditto
        (pushSourceRange): ditto
        (expandReplacements): ditto
        (pushReplacement): ditto
        * kjs/ustring.cpp:
	(KJS::UString::spliceSubstringsWithSeparators): New method that
	pieces together substring ranges of this string together with
	specified separators, all at one go.
        * kjs/ustring.h:
        (KJS::UString::Range::Range): Added new helper class to represent
	substring choices.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@7564 268f45cc-cd09-0410-ab3c-d52691b4dbfc