Add toStdString methods to CString and WTF::String

third_party/WebKit/Source/wtf/text/WTFString.h

Index: third_party/WebKit/Source/wtf/text/WTFString.h
diff --git a/third_party/WebKit/Source/wtf/text/WTFString.h b/third_party/WebKit/Source/wtf/text/WTFString.h
index 256abc6a131a9904461570997cf74da03650d099..b2ee6852357237905b3e7909135cd467b2389b43 100644
--- a/third_party/WebKit/Source/wtf/text/WTFString.h
+++ b/third_party/WebKit/Source/wtf/text/WTFString.h
@@ -179,6 +179,8 @@ public:
     CString latin1() const;
     CString utf8(UTF8ConversionMode = LenientUTF8Conversion) const;
 
+    std::string toUTF8() const;

[Mikhail, 2015/09/30 14:02:01]

why not toStdString() ?

[Primiano Tucci (use gerrit), 2015/09/30 15:08:28]

AFAIK technically speaking std::string does not mandate a specific encoding [1],
so toStdString wouldn't explain what encoding the caller should expect.
More specifically, if you construct a WTF::String out of a UTF-16 string
[0x20AC, 0xD801], I could expect a toStdString() to just return a string
containing 4 bytes (0x20, 0xAC, 0xD8, 0x01), which is NOT the case here. What
you get is the equivalent UTF8 encoding of the same string (See the unittest)

[1] cplusplus.com says "If used to handle sequences of multi-byte or
variable-length characters", http://www.cplusplus.com/reference/string/string/

[Mikhail, 2015/09/30 15:58:39]

Agree, however having both 'CString utf8()' and 'std::string toUTF8()' at the
same time looks a bit awkward. Also 'to' prefix usually implies casting to a
type and here we just create a new 'std::string' instance. Maybe
'utf8StdString()' or smth. like that?

[Primiano Tucci (use gerrit), 2015/09/30 16:03:37]

Hmm ok for the StdString part, but I'd keep the to.
In my mind "to" implies a transformation, without to I expect it to be a trivial
operation / casting.
How about toUTF8StdString() ?

+
     UChar operator[](unsigned index) const
     {
         if (!m_impl || index >= m_impl->length())