Use LocalStyleChange for updating :-webkit-drag.

Source/core/css/DragUpdateTest.cpp

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "config.h"
+#include "core/dom/Element.h"
+#include "core/frame/FrameView.h"
+#include "core/html/HTMLDocument.h"
+#include "core/html/HTMLElement.h"
+#include "core/testing/DummyPageHolder.h"
+#include <gtest/gtest.h>
+
+using namespace WebCore;
+
+namespace {
+
+TEST(DragUpdateTest, AffectedByDragUpdate)
+{
+    // Check that when dragging the div in the document below, you only get a
+    // single element style recalc.
+
+    OwnPtr<DummyPageHolder> dummyPageHolder = DummyPageHolder::create(IntSize(800, 600));
+    HTMLDocument* document = toHTMLDocument(&dummyPageHolder->document());
+    document->documentElement()->setInnerHTML("<style>div {width:100px;height:100px} div:-webkit-drag { background-color: green }</style>"
+        "<div>"
+        "<span></span>"
+        "<span></span>"
+        "<span></span>"
+        "<span></span>"
+        "</div>", ASSERT_NO_EXCEPTION);
+
+    document->view()->updateLayoutAndStyleIfNeededRecursive();

[ojan, 2014/02/07 20:52:46]

Not sure it really matters, but I think you could just call
document->updateLayout() here and below.

[rune, 2014/02/07 21:53:17]

Done.

+    unsigned startCount = document->styleEngine()->resolverAccessCount();
+
+    document->documentElement()->renderer()->updateDragState(true);
+    document->view()->updateLayoutAndStyleIfNeededRecursive();
+
+    unsigned accessCount = document->styleEngine()->resolverAccessCount() - startCount;
+
+    ASSERT_EQ(1U, accessCount);
+}
+
+TEST(DragUpdateTest, ChildrenAffectedByDragUpdate)
+{
+    // Check that when dragging the div in the document below, you get a
+    // full subtree style recalc.
+
+    OwnPtr<DummyPageHolder> dummyPageHolder = DummyPageHolder::create(IntSize(800, 600));
+    HTMLDocument* document = toHTMLDocument(&dummyPageHolder->document());
+    document->documentElement()->setInnerHTML("<style>div {width:100px;height:100px} div:-webkit-drag span { background-color: green }</style>"
+        "<div>"
+        "<span></span>"
+        "<span></span>"
+        "<span></span>"
+        "<span></span>"
+        "</div>", ASSERT_NO_EXCEPTION);
+
+    document->view()->updateLayoutAndStyleIfNeededRecursive();
+    unsigned startCount = document->styleEngine()->resolverAccessCount();
+
+    document->documentElement()->renderer()->updateDragState(true);
+    document->view()->updateLayoutAndStyleIfNeededRecursive();
+
+    unsigned accessCount = document->styleEngine()->resolverAccessCount() - startCount;
+
+    ASSERT_EQ(5U, accessCount);
+}
+
+} // namespace