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
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index 0000000000000000000000000000000000000000..47a440374ce1398870c7f9bddba80b699b9bf071
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+++ b/third_party/WebKit/Source/core/page/scrolling/SnapCoordinator.h
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+// 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"
+#include "platform/heap/Handle.h"
+#include "platform/scroll/ScrollTypes.h"
+#include "wtf/PassRefPtr.h"
+#include "wtf/RefCounted.h"
+#include "wtf/Vector.h"
+
+namespace blink {
+
+using SnapElementSet = WillBeHeapHashSet<RawPtrWillBeWeakMember<const Element>>;
+using SnapElementMap = WillBeHeapHashMap<RawPtrWillBeWeakMember<const Element>, OwnPtrWillBeMember<SnapElementSet>>;
+
+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(const Element&, ScrollSnapType);
+    void snapElementDidChange(const Element&, Vector<LengthPoint> snapCoordinates);
+
+#ifndef NDEBUG
+    void showSnapElementMap();
+    void showSnapElementsFor(const Element*);
+#endif
+
+private:
+    friend class SnapCoordinatorTest;
+    explicit SnapCoordinator();
+
+    Vector<double> snapOffsets(const Element&, ScrollbarOrientation);
+    const Element* findSnapContainer(const Element&);
+    void addSnapContainer(const Element&);
+    void addSnapElement(const Element&, const Element&);
+    void removeSnapContainer(const Element&);
+    void removeSnapElement(const Element&);
+
+    SnapElementSet& ensureSnapElementSet(const Element&);
+
+    SnapElementMap m_elementMap;
+};
+
+} // namespace blink
+
+#endif // SnapCoordinator_h