views: Mark single-argument constructors as explicit.

ui/views/bubble/bubble_frame_view_unittest.cc

Index: ui/views/bubble/bubble_frame_view_unittest.cc
diff --git a/ui/views/bubble/bubble_frame_view_unittest.cc b/ui/views/bubble/bubble_frame_view_unittest.cc
index 387bf52a40bd23cf1be9531a59414e5ea6147960..cb99f07d07e274826977524aa77eb839dc8f538c 100644
--- a/ui/views/bubble/bubble_frame_view_unittest.cc
+++ b/ui/views/bubble/bubble_frame_view_unittest.cc
@@ -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.
 
@@ -40,7 +40,7 @@ gfx::Size SizedBubbleDelegateView::GetPreferredSize() { return kRect.size(); }
 
 class TestBubbleFrameView : public BubbleFrameView {
  public:
-  TestBubbleFrameView(const gfx::Rect& bounds);
+  explicit TestBubbleFrameView(const gfx::Rect& bounds);
   virtual ~TestBubbleFrameView();
 
  protected: