Replace OS::MemCopy with OS::MemMove (just as fast but more flexible).

src/string-stream.cc

Index: src/string-stream.cc
diff --git a/src/string-stream.cc b/src/string-stream.cc
index bcc30f9ab372dd46605c95fe9bf3faf9d914840d..61eec0d696d52fa10a0a439d38fdfd8640efa936 100644
--- a/src/string-stream.cc
+++ b/src/string-stream.cc
@@ -254,7 +254,7 @@ void StringStream::Add(const char* format, FmtElm arg0, FmtElm arg1,
 
 SmartArrayPointer<const char> StringStream::ToCString() const {
   char* str = NewArray<char>(length_ + 1);
-  memcpy(str, buffer_, length_);
+  OS::MemCopy(str, buffer_, length_);
   str[length_] = '\0';
   return SmartArrayPointer<const char>(str);
 }
@@ -575,7 +575,7 @@ char* HeapStringAllocator::grow(unsigned* bytes) {
   if (new_space == NULL) {
     return space_;
   }
-  memcpy(new_space, space_, *bytes);
+  OS::MemCopy(new_space, space_, *bytes);
   *bytes = new_bytes;
   DeleteArray(space_);
   space_ = new_space;