Add NormalizingInputFilterWin to un-pick AltGr sequences.

remoting/client/normalizing_input_filter_win.h

Index: remoting/client/normalizing_input_filter_win.h
diff --git a/remoting/client/normalizing_input_filter_win.h b/remoting/client/normalizing_input_filter_win.h
new file mode 100644
index 0000000000000000000000000000000000000000..e4c2f95a1eaf74e3fc308f18f78e7c496913692f
--- /dev/null
+++ b/remoting/client/normalizing_input_filter_win.h
@@ -0,0 +1,60 @@
+// 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 REMOTING_CLIENT_NORMALIZING_INPUT_FILTER_WIN_H_
+#define REMOTING_CLIENT_NORMALIZING_INPUT_FILTER_WIN_H_
+
+#include "base/macros.h"
+#include "remoting/proto/event.pb.h"
+#include "remoting/protocol/input_filter.h"
+
+namespace remoting {
+
+// NormalizingInputFilterWin works around a quirk in Windows' handling of the
+// AltGr key.  When using a layout that treats RightAlt as AltGr, Windows
+// generates the following for an AltGr keydown/keyup cycle:
+//
+//   keydown LeftControl
+//   keydown RightAlt
+//   keyup LeftControl
+//   keyup RightAlt
+//
+// In a layout without AltGr the key will generate only RightAlt events.
+//
+// This filter captures LeftControl keydown events and defers them until
+// some other event occurs; if the next event is a RightAlt keydown then
+// the LeftControl is ignored and neither keydown nor keyup will be sent
+// for it.
+class NormalizingInputFilterWin : public protocol::InputFilter {
+ public:
+  explicit NormalizingInputFilterWin(protocol::InputStub* input_stub);
+  ~NormalizingInputFilterWin() override;
+
+  // InputFilter interface.
+  void InjectKeyEvent(const protocol::KeyEvent& event) override;
+  void InjectMouseEvent(const protocol::MouseEvent& event) override;
+
+ private:
+  void ProcessKeyDown(const protocol::KeyEvent& event);
+  void ProcessKeyUp(const protocol::KeyEvent& event);
+
+  // Sends the |deferred_control_keydown_|, if any, and clears it.
+  void FlushDeferredKeydownEvent();
+
+  // Holds the keydown event for LeftControl immediately after it has been
+  // pressed, until we have determined whether it is part of AltGr.
+  protocol::KeyEvent deferred_control_keydown_;
+
+  // True if LeftControl is pressed and treated as LeftControl.
+  bool left_control_is_pressed_ = false;
+
+  // True if LeftControl is pressed as part of AltGr.
+  bool altgr_is_pressed_ = false;
+
+  DISALLOW_COPY_AND_ASSIGN(NormalizingInputFilterWin);
+};
+
+}  // namespace remoting
+
+#endif  // REMOTING_CLIENT_NORMALIZING_INPUT_FILTER_WIN_H_