[SharedArrayBuffer] Add "AllowShared" extended attribute, used for WebGL

third_party/WebKit/Source/platform/wtf/typed_arrays/TypedArrayBase.h

Index: third_party/WebKit/Source/platform/wtf/typed_arrays/TypedArrayBase.h
diff --git a/third_party/WebKit/Source/platform/wtf/typed_arrays/TypedArrayBase.h b/third_party/WebKit/Source/platform/wtf/typed_arrays/TypedArrayBase.h
index 5b024e0eeb4e1e6d20c73d481c1f12244f37e43d..415529dba40b636bed52a2069fbf2b202f62f152 100644
--- a/third_party/WebKit/Source/platform/wtf/typed_arrays/TypedArrayBase.h
+++ b/third_party/WebKit/Source/platform/wtf/typed_arrays/TypedArrayBase.h
@@ -38,6 +38,9 @@ class TypedArrayBase : public ArrayBufferView {
   typedef T ValueType;
 
   T* Data() const { return static_cast<T*>(BaseAddress()); }
+  T* DataMaybeShared() const {
+    return static_cast<T*>(BaseAddressMaybeShared());
+  }
 
   bool Set(TypedArrayBase<T>* array, unsigned offset) {
     return SetImpl(array, offset * sizeof(T));