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 8662311cb4b5fa6049197c83f1988d96e21b8e52..b8f9ee92ff46c7bfb7ebf8a0d71f671483fe92e0 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)                                                                \
@@ -718,6 +719,16 @@ 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);