[Mac] Avoid "adding unknown subview" warning.

chrome/browser/ui/cocoa/tabs/tab_strip_controller.mm

Index: chrome/browser/ui/cocoa/tabs/tab_strip_controller.mm
diff --git a/chrome/browser/ui/cocoa/tabs/tab_strip_controller.mm b/chrome/browser/ui/cocoa/tabs/tab_strip_controller.mm
index 626d742e101675067ae37c08e24de353f009093a..d380384d8778ccfec5f89e8513b72c61afc6de5f 100644
--- a/chrome/browser/ui/cocoa/tabs/tab_strip_controller.mm
+++ b/chrome/browser/ui/cocoa/tabs/tab_strip_controller.mm
@@ -144,6 +144,14 @@ CGFloat FlipXInView(NSView* view, CGFloat width, CGFloat x) {
 
 }  // namespace
 
+@interface NSView (PrivateAPI)
+// Called by AppKit to check if dragging this view should move the window.
+// NSButton overrides this method in the same way so dragging window buttons
+// has no effect. NSView implementation returns NSZeroRect so the whole view
+// area can be dragged.
+- (NSRect)_opaqueRectForWindowMoveWhenInTitlebar;
+@end
+
 @interface TabStripController (Private)
 - (void)addSubviewToPermanentList:(NSView*)aView;
 - (void)regenerateSubviewList;
@@ -229,6 +237,10 @@ CGFloat FlipXInView(NSView* view, CGFloat width, CGFloat x) {
   return NO;
 }
 
+- (NSRect)_opaqueRectForWindowMoveWhenInTitlebar {
+ return [self bounds];
+}
+
 - (id)initWithFrame:(NSRect)frameRect
          controller:(TabStripController*)controller {
   if ((self = [super initWithFrame:frameRect])) {