Zero-sized windows are bad.

ui/base/cocoa/underlay_opengl_hosting_window.mm

 // 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.
 
 #import "ui/base/cocoa/underlay_opengl_hosting_window.h"
 
 #import <objc/runtime.h>
 
 #include "base/logging.h"
 #include "base/mac/mac_util.h"
@@ skipping 69 matching lines @@
                                   reinterpret_cast<IMP>(&RootDidAddSubview),
                                   method_getTypeEncoding(m));
     DCHECK(didAdd);
   }
 }
 
 - (id)initWithContentRect:(NSRect)contentRect
                 styleMask:(NSUInteger)windowStyle
                   backing:(NSBackingStoreType)bufferingType
                     defer:(BOOL)deferCreation {
+  // It is invalid to create windows with zero width or height. It screws things
+  // up royally:
+  // - It causes console spew: <http://crbug.com/78973>
+  // - It breaks Expose: <http://sourceforge.net/projects/heat-meteo/forums/forum/268087/topic/4582610>
+  //
+  // This is a banned practice
+  // <http://www.chromium.org/developers/coding-style/cocoa-dos-and-donts>. Do
+  // not do this. Use kWindowSizeDeterminedLater in
+  // ui/base/cocoa/window_size_constants.h instead.
+  //
+  // (This is checked here because UnderlayOpenGLHostingWindow is the base of
+  // most Chromium windows, not because this is related to its functionality.)
+  DCHECK(contentRect.size.width > 0 &&
+         contentRect.size.height > 0);
   if ((self = [super initWithContentRect:contentRect
                                styleMask:windowStyle
                                  backing:bufferingType
                                    defer:deferCreation])) {
     // The invisible opaque area technique only works > 10.5. Fortunately, hole
     // punching is used only when IOSurfaces are used to transport, and that's
     // also only on > 10.5. Also, don't mess around with things if it's not a
     // proper window with a title bar and all.
     if (base::mac::IsOSSnowLeopardOrLater() &&
         windowStyle && NSTitledWindowMask) {
@@ skipping 19 matching lines @@
       [rightOpaque setAutoresizingMask:NSViewMinXMargin | NSViewHeightSizable];
       [rightOpaque setAlphaValue:kAlphaValueJustOpaqueEnough];
       [rootView addSubview:rightOpaque];
     }
   }
 
   return self;
 }
 
 @end