[mac] Fixed window buttons positioning on Sierra.

chrome/browser/ui/cocoa/framed_browser_window.mm

Index: chrome/browser/ui/cocoa/framed_browser_window.mm
diff --git a/chrome/browser/ui/cocoa/framed_browser_window.mm b/chrome/browser/ui/cocoa/framed_browser_window.mm
index 9daf43125cdeca54da06f1ff72b58a9c421afa44..2bd1cf99cc4baa9e22f5aacc6f1023b65f500a18 100644
--- a/chrome/browser/ui/cocoa/framed_browser_window.mm
+++ b/chrome/browser/ui/cocoa/framed_browser_window.mm
@@ -40,6 +40,7 @@
     MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_11
 @interface NSObject (NSLayoutConstraint)
 - (NSLayoutConstraint*)constraintEqualToAnchor:(id)anchor constant:(CGFloat)c;
+- (NSLayoutConstraint*)constraintEqualToAnchor:(id)anchor;
 @end
 #endif
 
@@ -285,6 +286,10 @@ const CGFloat kWindowGradientHeight = 24.0;
   [[leadingSourceAnchorDuck constraintEqualToAnchor:leadingTargetAnchor
                                            constant:leadingOffset]
       setActive:YES];
+
+  [[[button bottomAnchor]
+      constraintEqualToAnchor:[[button superview] bottomAnchor]]
+          setActive:YES];
 }
 
 - (void)adjustCloseButton:(NSNotification*)notification {