Keep a cache of caret painters to avoid recomputing all the time.

Source/core/paint/PaintDataCache.h

Index: Source/core/paint/PaintDataCache.h
diff --git a/Source/core/paint/PaintDataCache.h b/Source/core/paint/PaintDataCache.h
new file mode 100644
index 0000000000000000000000000000000000000000..e7a0c54b7a275d062755cc7c5d84a9ce9ef091c7
--- /dev/null
+++ b/Source/core/paint/PaintDataCache.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 PaintDataCache_h
+#define PaintDataCache_h
+
+#include "core/layout/LayoutBlock.h"
+
+namespace blink {
+
+class LocalFrame;
+
+// Caches information computed during paint which is likely to be reused again.
+// Purely an optimization, and not expected to outlive a high-level paint.
+class PaintDataCache {
+public:
+    bool layoutBlockHasCaret(const LayoutBlock& layoutBlock)
+    {
+        LocalFrame* frame = layoutBlock.frame();
+        if (m_caretFrame != frame)
+            updateCaretCacheForFrame(frame);
+        return &layoutBlock == m_cursorCaretLayoutObject || &layoutBlock == m_dragCaretLayoutObject;
+    }
+
+    void getLayoutBlockCarets(const LayoutBlock& layoutBlock, bool* hasCursorCaret, bool* hasDragCaret)
+    {
+        LocalFrame* frame = layoutBlock.frame();
+        if (m_caretFrame != frame)
+            updateCaretCacheForFrame(frame);
+        *hasCursorCaret = &layoutBlock == m_cursorCaretLayoutObject;
+        *hasDragCaret = &layoutBlock == m_dragCaretLayoutObject;
+    }
+
+private:
+    void updateCaretCacheForFrame(const LocalFrame*);
+
+    // Used to quickly check which layout objects paint carets.
+    const LocalFrame* m_caretFrame = nullptr;
+    const LayoutBlock* m_cursorCaretLayoutObject = nullptr;
+    const LayoutBlock* m_dragCaretLayoutObject = nullptr;
+};
+
+} // namespace blink
+
+#endif // PaintDataCache_h