Add the allocator intrinsics for dart:typeddata implementation.

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 19729)
+++ runtime/vm/object.h	(working copy)
@@ -4972,6 +4972,11 @@
     return element_size[class_id - kTypedDataInt8ArrayCid];
   }
 
+  static intptr_t MaxElements(intptr_t class_id) {
+    ASSERT(RawObject::IsTypedDataClassId(class_id));
+    return (kSmiMax / ElementSizeInBytes(class_id));
+  }
+
   static RawTypedData* New(intptr_t class_id,
                            intptr_t len,
                            Heap::Space space = Heap::kNew);
@@ -5050,6 +5055,11 @@
     return TypedData::element_size[class_id - kExternalTypedDataInt8ArrayCid];
   }
 
+  static intptr_t MaxElements(intptr_t class_id) {
+    ASSERT(RawObject::IsExternalTypedDataClassId(class_id));
+    return (kSmiMax / ElementSizeInBytes(class_id));
+  }
+
   static RawExternalTypedData* New(intptr_t class_id,
                                    uint8_t* data,
                                    intptr_t len,