Start a drag if the tab is dragged off the sides of the window....

chrome/browser/cocoa/tab_strip_controller.h

 // Copyright (c) 2009 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 CHROME_BROWSER_COCOA_TAB_STRIP_CONTROLLER_H_
 #define CHROME_BROWSER_COCOA_TAB_STRIP_CONTROLLER_H_
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/scoped_nsobject.h"
@@ skipping 102 matching lines @@
 
 // return the view at a given index
 - (NSView*)viewAtIndex:(NSUInteger)index;
 
 // Set the placeholder for a dragged tab, allowing the |frame| and |strechiness|
 // to be specified. This causes this tab to be rendered in an arbitrary position
 - (void)insertPlaceholderForTab:(TabView*)tab
                           frame:(NSRect)frame
                   yStretchiness:(CGFloat)yStretchiness;
 
+// Returns whether or not |tab| can still be fully seen in the tab strip or if
+// its current position would cause it be obscured by things such as the edge
+// of the window or the window decorations. Returns YES only if the entire tab
+// is visible.
+- (BOOL)isTabFullyVisible:(TabView*)tab;
+
 // Show or hide the new tab button. The button is hidden immediately, but
 // waits until the next call to |-layoutTabs| to show it again.
 - (void)showNewTabButton:(BOOL)show;
 
 // Force the tabs to rearrange themselves to reflect the current model.
 - (void)layoutTabs;
 
 // The user changed the theme, or theme state changed.
 - (void)applyTheme;
 
@@ skipping 12 matching lines @@
 - (void)attachConstrainedWindow:(ConstrainedWindowMac*)window;
 - (void)removeConstrainedWindow:(ConstrainedWindowMac*)window;
 
 @end
 
 // Notification sent when the number of tabs changes. The object will be this
 // controller.
 extern NSString* const kTabStripNumberOfTabsChanged;
 
 #endif  // CHROME_BROWSER_COCOA_TAB_STRIP_CONTROLLER_H_