Make UTF8ToWide take a StringPiece, to avoid copying to a std::string.

base/string_util.h

Index: base/string_util.h
diff --git a/base/string_util.h b/base/string_util.h
index 3f905fe6f0a11f10f177b1c25e9c269a815ffab7..04c43229d8d1066015ffde0b85e5ee1530954983 100644
--- a/base/string_util.h
+++ b/base/string_util.h
@@ -14,6 +14,7 @@
 
 #include "base/basictypes.h"
 #include "base/string16.h"
+#include "base/string_piece.h"  // For implicit conversions.
 
 // Safe standard library wrappers for all platforms.
 
@@ -173,7 +174,7 @@ string16 ASCIIToUTF16(const std::string& ascii);
 bool WideToUTF8(const wchar_t* src, size_t src_len, std::string* output);
 std::string WideToUTF8(const std::wstring& wide);
 bool UTF8ToWide(const char* src, size_t src_len, std::wstring* output);
-std::wstring UTF8ToWide(const std::string& utf8);
+std::wstring UTF8ToWide(const StringPiece& utf8);
 
 bool WideToUTF16(const wchar_t* src, size_t src_len, string16* output);
 string16 WideToUTF16(const std::wstring& wide);