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

chrome/browser/cocoa/tab_window_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_TAB_WINDOW_CONTROLLER_H_
 #define CHROME_BROWSER_TAB_WINDOW_CONTROLLER_H_
 
 // A class acting as the Objective-C window controller for a window that has
 // tabs which can be dragged around. Tabs can be re-arranged within the same
 // window or dragged into other TabWindowController windows. This class doesn't
@@ skipping 55 matching lines @@
 
 // Removes the placeholder installed by |-insertPlaceholderForTab:atLocation:|
 // and restores the new tab button. Subclasses need to call the superclass
 // implementation.
 - (void)removePlaceholder;
 
 // 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;
 
+// 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. The default implementation always returns YES.
+- (BOOL)isTabFullyVisible:(TabView*)tab;
+
 // Called to check if the receiver can receive dragged tabs from
 // source.  Return YES if so.  The default implementation returns NO.
 - (BOOL)canReceiveFrom:(TabWindowController*)source;
 
 // Move a given tab view to the location of the current placeholder. If there is
 // no placeholder, it will go at the end. |controller| is the window controller
 // of a tab being dropped from a different window. It will be nil if the drag is
 // within the window, otherwise the tab is removed from that window before being
 // placed into this one. The implementation will call |-removePlaceholder| since
 // the drag is now complete.  This also calls |-layoutTabs| internally so
@@ skipping 26 matching lines @@
 // can override this to add more things besides the tab strip. Be sure to
 // call the superclass' version if overridden.
 - (NSArray*)viewsToMoveToOverlay;
 
 // Tells the tab strip to forget about this tab in preparation for it being
 // put into a different tab strip, such as during a drop on another window.
 - (void)detachTabView:(NSView*)view;
 @end
 
 #endif  // CHROME_BROWSER_TAB_WINDOW_CONTROLLER_H_