Compute snap offsets (both repeat and element based)

third_party/WebKit/Source/core/page/scrolling/SnapCoordinator.h

Index: third_party/WebKit/Source/core/page/scrolling/SnapCoordinator.h
diff --git a/third_party/WebKit/Source/core/page/scrolling/SnapCoordinator.h b/third_party/WebKit/Source/core/page/scrolling/SnapCoordinator.h
new file mode 100644
index 0000000000000000000000000000000000000000..99de521b22df7dad511fb9d4aea72c1f30e37f9a
--- /dev/null
+++ b/third_party/WebKit/Source/core/page/scrolling/SnapCoordinator.h
@@ -0,0 +1,52 @@
+// Copyright 2015 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 SnapCoordinator_h
+#define SnapCoordinator_h
+
+#include "core/dom/Element.h"

[esprehn, 2015/12/01 18:31:12]

can you forward declare more of this?

[majidvp, 2015/12/03 17:54:17]

Done.

+#include "core/layout/LayoutBox.h"
+#include "platform/heap/Handle.h"
+#include "platform/scroll/ScrollTypes.h"
+#include "wtf/PassRefPtr.h"
+#include "wtf/RefCounted.h"
+#include "wtf/Vector.h"
+
+namespace blink {
+
+class ComputedStyle;
+struct LengthPoint;
+
+// Snap Coordinator keeps track of snap containers and all of their associated
+// snap elements. It also contains the logic to generate the final list of snap
+// offsets for any snap container.
+class CORE_EXPORT SnapCoordinator final : public NoBaseWillBeGarbageCollected<SnapCoordinator> {
+    WTF_MAKE_NONCOPYABLE(SnapCoordinator);
+
+public:
+    static PassOwnPtrWillBeRawPtr<SnapCoordinator> create();
+    ~SnapCoordinator();
+    DEFINE_INLINE_TRACE() {}
+
+    void snapContainerDidChange(LayoutBox&, ScrollSnapType);
+    void snapAreaDidChange(LayoutBox&, const Vector<LengthPoint>& snapCoordinates);
+
+#ifndef NDEBUG
+    void showSnapAreaMap();
+    void showSnapAreasFor(const LayoutBox*);
+#endif
+
+private:
+    friend class SnapCoordinatorTest;
+    explicit SnapCoordinator();
+
+    Vector<double> snapOffsets(const Element&, ScrollbarOrientation);
+    LayoutBox* findSnapContainer(const LayoutBox&);
+
+    WillBeHeapHashSet<RawPtrWillBeWeakMember<const LayoutBox>> m_snapContainers;
+};
+
+} // namespace blink
+
+#endif // SnapCoordinator_h