Introduce BackspaceStateMachine

third_party/WebKit/Source/core/editing/BackspaceStateMachine.h

+// Copyright 2016 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 BackspaceStateMachine_h
+#define BackspaceStateMachine_h
+
+#include "core/CoreExport.h"
+#include "wtf/Allocator.h"
+#include "wtf/Noncopyable.h"
+#include "wtf/text/Unicode.h"
+
+namespace blink {
+
+class CORE_EXPORT BackspaceStateMachine {
+    STACK_ALLOCATED();
+    WTF_MAKE_NONCOPYABLE(BackspaceStateMachine);
+public:
+    BackspaceStateMachine() = default;
+
+    // Returns true when the state machine has stopped.
+    bool updateState(UChar codeUnit);
+
+    // Finalize the state machine and returns the code unit count to be deleted.
+    // If the state machine hasn't finished, this method finishes the state
+    // machine first.
+    int finalizeAndGetCodeUnitCountToBeDeleted();
+
+    // Resets the internal state to the initial state.
+    void reset();
+
+private:
+    int m_codeUnitsToBeDeleted = 0;
+
+    // Used for composing supplementary code point with surrogate pairs.
+    UChar m_trailSurrogate = 0;
+};
+
+} // namespace blink
+
+#endif