Move StringPiece into the base namespace. It is colliding

base/string_util_icu.cc

Index: base/string_util_icu.cc
diff --git a/base/string_util_icu.cc b/base/string_util_icu.cc
index a043e9711a6c0d043bc4a7bfc85b211ac3254da3..d3c9edf2eed4c55e8b8ff8c22ea38bb3fe09960e 100644
--- a/base/string_util_icu.cc
+++ b/base/string_util_icu.cc
@@ -333,7 +333,7 @@ bool WideToUTF8(const wchar_t* src, size_t src_len, std::string* output) {
   return ConvertUnicode<wchar_t, std::string>(src, src_len, output);
 }
 
-std::wstring UTF8ToWide(const StringPiece& utf8) {
+std::wstring UTF8ToWide(const base::StringPiece& utf8) {
   std::wstring ret;
   if (utf8.empty())
     return ret;