Move a few functions commonly called with char* to StringPiece.

base/string_util.h

Index: base/string_util.h
diff --git a/base/string_util.h b/base/string_util.h
index f40cc8dc0056a6c07424442dc24434855aba4a93..b082078117ee126ae1a20d4231b74d933426bbc5 100644
--- a/base/string_util.h
+++ b/base/string_util.h
@@ -174,9 +174,9 @@ std::wstring CollapseWhitespace(const std::wstring& text,
 
 // These convert between ASCII (7-bit) and Wide/UTF16 strings.
 std::string WideToASCII(const std::wstring& wide);
-std::wstring ASCIIToWide(const std::string& ascii);
+std::wstring ASCIIToWide(const StringPiece& ascii);
 std::string UTF16ToASCII(const string16& utf16);
-string16 ASCIIToUTF16(const std::string& ascii);
+string16 ASCIIToUTF16(const StringPiece& ascii);
 
 // These convert between UTF-8, -16, and -32 strings. They are potentially slow,
 // so avoid unnecessary conversions. The low-level versions return a boolean
@@ -252,7 +252,7 @@ bool IsString8Bit(const std::wstring& str);
 bool IsStringUTF8(const std::string& str);
 bool IsStringWideUTF8(const std::wstring& str);
 bool IsStringASCII(const std::wstring& str);
-bool IsStringASCII(const std::string& str);
+bool IsStringASCII(const StringPiece& str);
 bool IsStringASCII(const string16& str);
 
 // ASCII-specific tolower.  The standard library's tolower is locale sensitive,