Add an external array type to support typed arrays.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 59dee1d3f7d1faace9666048df7eb9fc1751a618..a7fa2f8ff6de44f883f148049fe3ebc4d2f89d24 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -2777,6 +2777,56 @@ class ImmutableArray : public Array {
 };
 
 
+class ByteBuffer : public Instance {
+ public:
+  intptr_t Length() const {
+    ASSERT(!IsNull());
+    return Smi::Value(raw_ptr()->length_);
+  }
+
+  template<typename T>
+  T At(intptr_t index) const {
+    return *Addr<T>(index);
+  }
+  template<typename T>
+  void SetAt(intptr_t index, T value) const {
+    *Addr<T>(index) = value;
+  }
+
+  virtual bool Equals(const Instance& other) const;
+
+  static intptr_t InstanceSize() {
+    return RoundedAllocationSize(sizeof(RawByteBuffer));
+  }
+
+  static RawByteBuffer* New(uint8_t* data,
+                            intptr_t len,
+                            Heap::Space space = Heap::kNew);
+
+ private:
+  template<typename T>
+  T* Addr(intptr_t index) const {
+    intptr_t base = index * sizeof(T);
+    intptr_t limit = base + sizeof(T);
+    // TODO(iposva): Determine if we should throw an exception here.
+    ASSERT((base >= 0) && (limit <= Length()));
+    uint8_t* addr = &raw_ptr()->data_[base];
+    return reinterpret_cast<T*>(addr);
+  }
+
+  void SetLength(intptr_t value) {
+    raw_ptr()->length_ = Smi::New(value);
+  }
+
+  void SetData(uint8_t* data) const {
+    raw_ptr()->data_ = data;
+  }
+
+  HEAP_OBJECT_IMPLEMENTATION(ByteBuffer, Instance);
+  friend class Class;
+};
+
+
 class Closure : public Instance {
  public:
   RawFunction* function() const { return raw_ptr()->function_; }