Add an external array type to support typed arrays.

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
diff --git a/runtime/vm/raw_object.h b/runtime/vm/raw_object.h
index 3e91d91e6dc8ba76ee498e71b164a6923b2d7a11..0525e8826fac57cabf91171f4201b19993fed47e 100644
--- a/runtime/vm/raw_object.h
+++ b/runtime/vm/raw_object.h
@@ -52,6 +52,7 @@ namespace dart {
     V(Bool)                                                                    \
     V(Array)                                                                   \
       V(ImmutableArray)                                                        \
+    V(ByteBuffer)                                                              \
     V(Closure)                                                                 \
     V(Stacktrace)                                                              \
     V(JSRegExp)                                                                \
@@ -719,6 +720,18 @@ class RawImmutableArray : public RawArray {
 };
 
 
+class RawByteBuffer : public RawInstance {
+  RAW_HEAP_OBJECT_IMPLEMENTATION(ByteBuffer);
+
+  RawObject** from() { return reinterpret_cast<RawObject**>(&ptr()->length_); }
+  RawSmi* length_;
+  RawObject** to() {
+    return reinterpret_cast<RawObject**>(&ptr()->length_);
+  }
+  uint8_t* data_;
+};
+
+
 class RawClosure : public RawInstance {
   RAW_HEAP_OBJECT_IMPLEMENTATION(Closure);