To ensure that the location bar will not reach the minimum width.

chrome/browser/ui/cocoa/extensions/browser_actions_container_view.mm

 // Copyright (c) 2011 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 "chrome/browser/ui/cocoa/extensions/browser_actions_container_view.h"
 
 #include <algorithm>
 
 #include "base/basictypes.h"
 #import "chrome/browser/ui/cocoa/view_id_util.h"
 
 NSString* const kBrowserActionGrippyDragStartedNotification =
     @"BrowserActionGrippyDragStartedNotification";
 NSString* const kBrowserActionGrippyDraggingNotification =
     @"BrowserActionGrippyDraggingNotification";
 NSString* const kBrowserActionGrippyDragFinishedNotification =
     @"BrowserActionGrippyDragFinishedNotification";
+NSString* const kBrowserActionGrippyWillDragNotification =
+    @"BrowserActionGrippyWillDragNotification";
+NSString* const kTranslationWithDelta =
+    @"TranslationWithDelta";
 
 namespace {
 const CGFloat kAnimationDuration = 0.2;
 const CGFloat kGrippyWidth = 4.0;
 const CGFloat kMinimumContainerWidth = 10.0;
 }  // namespace
 
 @interface BrowserActionsContainerView(Private)
 // Returns the cursor that should be shown when hovering over the grippy based
 // on |canDragLeft_| and |canDragRight_|.
@@ skipping 83 matching lines @@
 
   NSPoint location = [self convertPoint:[theEvent locationInWindow]
                                fromView:nil];
   NSRect containerFrame = [self frame];
   CGFloat dX = [theEvent deltaX];
   CGFloat withDelta = location.x - dX;
   canDragRight_ = (withDelta >= initialDragPoint_.x) &&
       (NSWidth(containerFrame) > kMinimumContainerWidth);
   canDragLeft_ = (withDelta <= initialDragPoint_.x) &&
       (NSWidth(containerFrame) < maxWidth_);
+
+  // Notify others to see whether this dragging is allowed.
+  if (canDragLeft_ || canDragRight_) {
+    NSDictionary* userInfo = @{ kTranslationWithDelta : @(dX) };
+    [[NSNotificationCenter defaultCenter]
+        postNotificationName:kBrowserActionGrippyWillDragNotification
+                      object:self
+                    userInfo:userInfo];
+  }
+
   if ((dX < 0.0 && !canDragLeft_) || (dX > 0.0 && !canDragRight_))
     return;
 
   containerFrame.size.width =
       std::max(NSWidth(containerFrame) - dX, kMinimumContainerWidth);
 
   if (NSWidth(containerFrame) == kMinimumContainerWidth)
     return;
 
   containerFrame.origin.x += dX;
@@ skipping 51 matching lines @@
     retVal = [NSCursor resizeRightCursor];
   } else if (!canDragRight_) {
     retVal = [NSCursor resizeLeftCursor];
   } else {
     retVal = [NSCursor resizeLeftRightCursor];
   }
   return retVal;
 }
 
 @end