Expose ArrayBufferView::HasBuffer

This allows the embedder to decide whether it's worthwhile to copy the
contents to avoid materializing a buffer.

BUG=v8:3996
R=dslomov@chromium.org,kbr@chromium.org
LOG=y

Review URL: https://codereview.chromium.org/1084513002

Cr-Commit-Position: refs/heads/master@{#27782}

include/v8.h

@@ -3511,6 +3511,12 @@ class V8_EXPORT ArrayBufferView : public Object {
    */
   size_t CopyContents(void* dest, size_t byte_length);
 
+  /**
+   * Returns true if ArrayBufferView's backing ArrayBuffer has already been
+   * allocated.
+   */
+  bool HasBuffer() const;
+
   V8_INLINE static ArrayBufferView* Cast(Value* obj);
 
   static const int kInternalFieldCount =

src/api.cc

@@ -6471,6 +6471,15 @@ size_t v8::ArrayBufferView::CopyContents(void* dest, size_t byte_length) {
 }
 
 
+bool v8::ArrayBufferView::HasBuffer() const {
+  i::Handle<i::JSArrayBufferView> obj = Utils::OpenHandle(this);
+  if (obj->IsJSDataView()) return true;
+  DCHECK(obj->IsJSTypedArray());
+  i::Handle<i::JSTypedArray> typed_array(i::JSTypedArray::cast(*obj));
+  return !typed_array->buffer()->IsSmi();
+}
+
+
 size_t v8::ArrayBufferView::ByteOffset() {
   i::Handle<i::JSArrayBufferView> obj = Utils::OpenHandle(this);
   return static_cast<size_t>(obj->byte_offset()->Number());

test/cctest/test-typedarrays.cc

@@ -19,22 +19,11 @@ void TestArrayBufferViewContents(LocalContext& env, bool should_use_buffer) {
   CHECK(obj_a->IsArrayBufferView());
   v8::Local<v8::ArrayBufferView> array_buffer_view =
       v8::Local<v8::ArrayBufferView>::Cast(obj_a);
-  Handle<JSArrayBufferView> internal_view(
-      v8::Utils::OpenHandle(*array_buffer_view));
-  bool has_buffer = true;
-  if (internal_view->IsJSTypedArray()) {
-    Handle<JSTypedArray> typed_array(JSTypedArray::cast(*internal_view));
-    has_buffer = !typed_array->buffer()->IsSmi();
-  }
-  CHECK_EQ(has_buffer, should_use_buffer);
+  CHECK_EQ(array_buffer_view->HasBuffer(), should_use_buffer);
   unsigned char contents[4] = {23, 23, 23, 23};
   CHECK_EQ(sizeof(contents),
            array_buffer_view->CopyContents(contents, sizeof(contents)));
-  if (!has_buffer) {
-    CHECK(internal_view->IsJSTypedArray());
-    Handle<JSTypedArray> typed_array(JSTypedArray::cast(*internal_view));
-    CHECK(typed_array->buffer()->IsSmi());
-  }
+  CHECK_EQ(array_buffer_view->HasBuffer(), should_use_buffer);
   for (size_t i = 0; i < sizeof(contents); ++i) {
     CHECK_EQ(i, contents[i]);
   }