Move ASCIIToWide and ASCIIToUTF16 to utf_string_conversions.h. I've found it...

base/utf_string_conversions.h

Index: base/utf_string_conversions.h
===================================================================
--- base/utf_string_conversions.h	(revision 54020)
+++ base/utf_string_conversions.h	(working copy)
@@ -48,4 +48,18 @@
 # define UTF16ToWideHack UTF16ToWide
 #endif
 
+// These convert an ASCII string, typically a hardcoded constant, to a
+// UTF16/Wide string.
+//
+// Note that this doesn't use StringPiece because it's very common to need
+// ASCIIToUTF16("foo"), and either we have to include it in this file, or
+// forward declare it and force all callers to include string_piece.h. Given
+// that string_piece brings in complicated stuff like <algorithm>, it's
+// easier to just duplicate these very simple definitions for the two calling
+// cases we actually use.
+std::wstring ASCIIToWide(const char* ascii);
+std::wstring ASCIIToWide(const std::string& ascii);
+string16 ASCIIToUTF16(const char* ascii);
+string16 ASCIIToUTF16(const std::string& ascii);
+
 #endif  // BASE_UTF_STRING_CONVERSIONS_H_