Make the edge where BackgroundGradientView draws a divider selectable.

chrome/browser/ui/cocoa/background_gradient_view.mm

Index: chrome/browser/ui/cocoa/background_gradient_view.mm
diff --git a/chrome/browser/ui/cocoa/background_gradient_view.mm b/chrome/browser/ui/cocoa/background_gradient_view.mm
index 6458533dbc51ed8db54c04fa93f229d46d37d96d..9eadb70752544a14ef7c061d419dee4890049ff3 100644
--- a/chrome/browser/ui/cocoa/background_gradient_view.mm
+++ b/chrome/browser/ui/cocoa/background_gradient_view.mm
@@ -12,14 +12,10 @@
 #import "ui/base/cocoa/nsview_additions.h"
 #include "ui/base/material_design/material_design_controller.h"
 
-@interface BackgroundGradientView (Private)
-- (void)commonInit;
-- (NSColor*)backgroundImageColor;
-@end
-
 @implementation BackgroundGradientView
 
 @synthesize showsDivider = showsDivider_;
+@synthesize dividerEdge = dividerEdge_;
 
 - (id)initWithFrame:(NSRect)frameRect {
   if ((self = [super initWithFrame:frameRect])) {
@@ -37,6 +33,7 @@
 
 - (void)commonInit {
   showsDivider_ = YES;
+  dividerEdge_ = NSMinYEdge;
 }
 
 - (void)setShowsDivider:(BOOL)show {
@@ -46,6 +43,13 @@
   [self setNeedsDisplay:YES];
 }
 
+- (void)setDividerEdge:(NSRectEdge)dividerEdge {
+  if (dividerEdge_ == dividerEdge)
+    return;
+  dividerEdge_ = dividerEdge;
+  [self setNeedsDisplay:YES];
+}
+
 - (NSPoint)patternPhase {
   return [[self window]
       themeImagePositionForAlignment:THEME_IMAGE_ALIGN_WITH_TAB_STRIP];
@@ -68,10 +72,10 @@
   NSRectFillUsingOperation(dirtyRect, NSCompositeSourceOver);
 
   if (showsDivider_) {
-    // Draw bottom stroke
+    // Draw stroke
     NSRect borderRect, contentRect;
     NSDivideRect([self bounds], &borderRect, &contentRect, [self cr_lineWidth],
-                 NSMinYEdge);
+                 dividerEdge_);
     if (NSIntersectsRect(borderRect, dirtyRect)) {
       [[self strokeColor] set];
       NSRectFillUsingOperation(NSIntersectionRect(borderRect, dirtyRect),