Make the browser->metro_viewer IPC channel name a constant instead of hardcoding it in a few places…

win8/viewer/metro_viewer_constants.h

Index: win8/viewer/metro_viewer_constants.h
diff --git a/win8/viewer/metro_viewer_constants.h b/win8/viewer/metro_viewer_constants.h
new file mode 100644
index 0000000000000000000000000000000000000000..bc0d904a78b28443710d5415695c3723a01cdbd0
--- /dev/null
+++ b/win8/viewer/metro_viewer_constants.h
@@ -0,0 +1,16 @@
+// Copyright (c) 2012 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 WIN8_VIEWER_METRO_VIEWER_CONSTANTS_H_
+#define WIN8_VIEWER_METRO_VIEWER_CONSTANTS_H_
+
+namespace win8 {
+
+// The name of the IPC channel between the browser process and the metro viewer
+// process.
+extern const char kMetroViewerIPCChannelName[];
+
+}  // namespace win8
+
+#endif  // WIN8_VIEWER_METRO_VIEWER_CONSTANTS_H_