https://bugs.webkit.org/show_bug.cgi?id=112957.

Reviewed by Geoffrey Garen.

The previous algorithm does a linear reverse scan of the source string
to find the line start for any given char position. This results in a
O(n^2) algortithm when the source string has no line breaks.

The new algorithm computes a line start column table for a
SourceProvider on first use. This line start table is used to fix up
op_debug's charPosition operand into a column operand when an
UnlinkedCodeBlock is linked into a CodeBlock. The initialization of
the line start table is O(n), and the CodeBlock column fix up is
O(log(n)).

* bytecode/CodeBlock.cpp:
(JSC::CodeBlock::dumpBytecode): 
(JSC::CodeBlock::CodeBlock): - do column fix up.
* interpreter/Interpreter.cpp:
(JSC::Interpreter::debug): - no need to do column fixup anymore.
* interpreter/Interpreter.h:
* jit/JITStubs.cpp:
(JSC::DEFINE_STUB_FUNCTION):
* llint/LLIntSlowPaths.cpp:
(JSC::LLInt::LLINT_SLOW_PATH_DECL):
* parser/SourceProvider.cpp:
(JSC::SourceProvider::lineStarts):
(JSC::charPositionExtractor):
(JSC::SourceProvider::charPositionToColumnNumber):
- initialize line start column table if needed.
- look up line start for the given char position.
* parser/SourceProvider.h:

Source/WTF: Introducing String::findNextLineStart().
https://bugs.webkit.org/show_bug.cgi?id=112957.

Reviewed by Geoffrey Garen.

This is replaces String::reverseFindLineTerminator() in the JSC
debugger's code for computing column numbers.

* wtf/text/StringImpl.cpp:
(WTF::StringImpl::findNextLineStart):
* wtf/text/StringImpl.h:
(WTF::findNextLineStart):
* wtf/text/WTFString.h:
(WTF::String::findNextLineStart):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@146552 268f45cc-cd09-0410-ab3c-d52691b4dbfc