Revert "Reworks the clipping logic" and follow-up.

Source/core/layout/ClipRectsCache.h

 // 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 ClipRectsCache_h
 #define ClipRectsCache_h
 
 #include "core/layout/ClipRects.h"
 
 #if ENABLE(ASSERT)
 #include "core/layout/LayoutBox.h" // For OverlayScrollbarSizeRelevancy.
 #endif
 
 namespace blink {
 
 class DeprecatedPaintLayer;
 
-// TODO: Because this is mostly empty, this should be moved to a better place
 enum ClipRectsCacheSlot {
     // Relative to the ancestor treated as the root (e.g. transformed layer). Used for hit testing.
     RootRelativeClipRects,
     RootRelativeClipRectsIgnoringViewportClip,
 
     // Relative to the LayoutView's layer. Used for compositing overlap testing.
-    // Computed during the compositing update step (see CompositingInputsUpdater::update).
     AbsoluteClipRects,
 
     // Relative to painting ancestor. Used for painting.
     PaintingClipRects,
     PaintingClipRectsIgnoringOverflowClip,
 
     NumberOfClipRectsCacheSlots,
     UncachedClipRects,
 };
 
+class ClipRectsCache {
+    WTF_MAKE_FAST_ALLOCATED(ClipRectsCache);
+public:
+    struct Entry {
+        Entry()
+            : root(nullptr)
+#if ENABLE(ASSERT)
+            , scrollbarRelevancy(IgnoreOverlayScrollbarSize)
+#endif
+        {
+        }
+        const DeprecatedPaintLayer* root;
+        RefPtr<ClipRects> clipRects;
+#if ENABLE(ASSERT)
+        OverlayScrollbarSizeRelevancy scrollbarRelevancy;
+#endif
+    };
+    Entry& get(ClipRectsCacheSlot slot)
+    {
+        ASSERT(slot < NumberOfClipRectsCacheSlots);
+        return m_entries[slot];
+    }
+    void clear(ClipRectsCacheSlot slot)
+    {
+        ASSERT(slot < NumberOfClipRectsCacheSlots);
+        m_entries[slot] = Entry();
+    }
+private:
+    Entry m_entries[NumberOfClipRectsCacheSlots];
+};
+
 } // namespace blink
 
 #endif // ClipRectsCache_h