Add key based scrolling on magnified screen for kiosk mode.

ash/magnifier/magnifier_key_scroller.h

Index: ash/magnifier/magnifier_key_scroller.h
diff --git a/ash/magnifier/magnifier_key_scroller.h b/ash/magnifier/magnifier_key_scroller.h
new file mode 100644
index 0000000000000000000000000000000000000000..4f9f19efb68367a96cbc9147ff1a6947c3611fd3
--- /dev/null
+++ b/ash/magnifier/magnifier_key_scroller.h
@@ -0,0 +1,67 @@
+// 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 ASH_MAGNIFIER_MAGNIFIER_KEY_SCROLLER_H_
+#define ASH_MAGNIFIER_MAGNIFIER_KEY_SCROLLER_H_
+
+#include "ash/ash_export.h"
+#include "ui/events/event_handler.h"
+
+namespace ui {
+class KeyEvent;
+}
+
+namespace ash {
+
+// This class implements the press and hold key-bindings (shift-arrow keys)
+// to control magnified screen.
+class ASH_EXPORT MagnifierKeyScroller : public ui::EventHandler {
+ public:
+  static bool IsEnabled();
+  static void SetEnabled(bool enabled);
+
+  MagnifierKeyScroller();
+  virtual ~MagnifierKeyScroller();
+
+  // ui::EventHandler overrides:
+  virtual void OnKeyEvent(ui::KeyEvent* key_event) OVERRIDE;
+
+  // A scoped object to enable and disable the magnifier accelerator for test.
+  class ScopedEnablerForTest {
+   public:
+    ScopedEnablerForTest() {
+      SetEnabled(true);
+    }
+    ~ScopedEnablerForTest() {
+      SetEnabled(false);
+    }
+
+   private:
+    DISALLOW_COPY_AND_ASSIGN(ScopedEnablerForTest);
+  };
+
+ private:
+  // A state to keep track of one click and click and hold operation.
+  //
+  // One click:
+  // INITIAL --(first press)--> PRESSED --(release)--> INITIAL[SEND PRESS]
+  //
+  // Click and hold:
+  // INITIAL --(first press)--> PRESSED --(press)-->
+  //   HOLD[scroll] --(press)--> HOLD[scroll] --(release)-->
+  //   INITIAL[stop scroll]
+  enum State {
+    INITIAL,
+    PRESSED,
+    HOLD
+  };
+
+  State state_;
+
+  DISALLOW_COPY_AND_ASSIGN(MagnifierKeyScroller);
+};
+
+}  // namespace ash
+
+#endif  // ASH_MAGNIFIER_MAGNIFIER_KEY_SCROLLER_H_