views: Mark single-argument constructors as explicit.

ui/views/paint_lock.h

Index: ui/views/paint_lock.h
diff --git a/ui/views/paint_lock.h b/ui/views/paint_lock.h
index 41e3083753d4070ece234ed5b8ee2aa5471ad839..23994193a5634b3d20e1f5c6a57ad0996a00a34b 100644
--- a/ui/views/paint_lock.h
+++ b/ui/views/paint_lock.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -22,7 +22,7 @@ class VIEWS_EXPORT PaintLock {
  public:
   // The paint lock does not own the view. It is an error for the view to be
   // destroyed before the lock.
-  PaintLock(View* view);
+  explicit PaintLock(View* view);
   ~PaintLock();
 
  private: