Reworked previous CL (ExternalStringGetPeer speed up) to avoid the

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
===================================================================
--- runtime/vm/dart_api_impl.cc	(revision 11534)
+++ runtime/vm/dart_api_impl.cc	(working copy)
@@ -1533,27 +1533,24 @@
     RETURN_NULL_ERROR(peer);
   } else {
     NoGCScope no_gc_scope;
-    RawObject* raw_obj = Api::UnwrapHandle(object);
+    uword raw_addr = RawObject::ToAddr(Api::UnwrapHandle(object));
     switch (class_id) {
       case kExternalOneByteStringCid: {
         RawExternalOneByteString* raw_string =
-            reinterpret_cast<RawExternalOneByteString*>(raw_obj)->ptr();
-        ExternalStringData<uint8_t>* data = raw_string->external_data_;
-        *peer = data->peer();
+            reinterpret_cast<RawExternalOneByteString*>(raw_addr);
+        *peer = raw_string->peer();
         return Api::Success(Isolate::Current());
       }
       case kExternalTwoByteStringCid: {
         RawExternalTwoByteString* raw_string =
-            reinterpret_cast<RawExternalTwoByteString*>(raw_obj)->ptr();
-        ExternalStringData<uint16_t>* data = raw_string->external_data_;
-        *peer = data->peer();
+            reinterpret_cast<RawExternalTwoByteString*>(raw_addr);
+        *peer = raw_string->peer();
         return Api::Success(Isolate::Current());
       }
       case kExternalFourByteStringCid: {
         RawExternalFourByteString* raw_string =
-            reinterpret_cast<RawExternalFourByteString*>(raw_obj)->ptr();
-        ExternalStringData<uint32_t>* data = raw_string->external_data_;
-        *peer = data->peer();
+            reinterpret_cast<RawExternalFourByteString*>(raw_addr);
+        *peer = raw_string->peer();
         return Api::Success(Isolate::Current());
       }
     }