Have srcset respond to viewport changes

Source/core/frame/ViewportChangeNotifier.h

Index: Source/core/frame/ViewportChangeNotifier.h
diff --git a/Source/core/frame/ViewportChangeNotifier.h b/Source/core/frame/ViewportChangeNotifier.h
new file mode 100644
index 0000000000000000000000000000000000000000..8722b3f24aface91a7b83cc42099f95cb78117c9
--- /dev/null
+++ b/Source/core/frame/ViewportChangeNotifier.h
@@ -0,0 +1,36 @@
+// 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.
+
+#ifndef ViewportChangeNotifier_h
+#define ViewportChangeNotifier_h
+
+#include "platform/heap/Handle.h"
+
+namespace WebCore {
+
+class ViewportChangeListener : public RefCountedWillBeGarbageCollected<ViewportChangeListener> {

[esprehn, 2014/07/14 08:39:49]

This is just a duplicate of what the mediaQuery thing already does.

+public:
+    virtual void viewportChanged() = 0;

[sof, 2014/07/14 20:38:08]

All classes that directly derive from a garbage collected class should define a
trace() method, so add

  virtual void trace(Visitor*) { }

+    DECLARE_EMPTY_VIRTUAL_DESTRUCTOR_WILL_BE_REMOVED(ViewportChangeListener);
+};
+
+class ViewportChangeNotifier : public NoBaseWillBeGarbageCollected<ViewportChangeNotifier> {
+public:
+    static PassOwnPtrWillBeRawPtr<ViewportChangeNotifier> create();
+    void addListener(ViewportChangeListener*);
+    void removeListener(ViewportChangeListener*);
+    void viewportChanged();
+
+    typedef WillBeHeapHashSet<RawPtrWillBeWeakMember<ViewportChangeListener> > ListenerContainer;
+
+private:
+    ViewportChangeNotifier() { };

[sof, 2014/07/14 20:38:09]

nit: redundant semicolon.

+    void trace(Visitor*);

[sof, 2014/07/14 20:38:08]

Make this a public method.

+
+    ListenerContainer m_listeners;
+};
+
+} // namespace
+
+#endif // MediaQueryBlockWatcher_h