Make the edge where BackgroundGradientView draws a divider selectable.

chrome/browser/ui/cocoa/download/download_shelf_view_cocoa.mm

Index: chrome/browser/ui/cocoa/download/download_shelf_view_cocoa.mm
diff --git a/chrome/browser/ui/cocoa/download/download_shelf_view_cocoa.mm b/chrome/browser/ui/cocoa/download/download_shelf_view_cocoa.mm
index 92dd23f985a34f5e67b16ecb8617858b0119cd8e..a6f6c0df825136975f48fff0164c3407a2fbda37 100644
--- a/chrome/browser/ui/cocoa/download/download_shelf_view_cocoa.mm
+++ b/chrome/browser/ui/cocoa/download/download_shelf_view_cocoa.mm
@@ -16,7 +16,7 @@
 // For programmatic instantiations in unit tests.
 - (id)initWithFrame:(NSRect)frameRect {
   if ((self = [super initWithFrame:frameRect])) {
-    [self setShowsDivider:NO];
+    self.dividerEdge = NSMaxYEdge;
   }
   return self;
 }
@@ -24,26 +24,11 @@
 // For nib instantiations in production.
 - (id)initWithCoder:(NSCoder*)decoder {
   if ((self = [super initWithCoder:decoder])) {
-    [self setShowsDivider:NO];
+    self.dividerEdge = NSMaxYEdge;
   }
   return self;
 }
 
-- (NSColor*)strokeColor {
-  const ui::ThemeProvider* themeProvider = [[self window] themeProvider];
-  if (!themeProvider) {
-    return [NSColor blackColor];
-  }
-  if (!ui::MaterialDesignController::IsModeMaterial()) {
-    BOOL isActive = [[self window] isMainWindow];
-    return themeProvider->GetNSColor(
-        isActive ? ThemeProperties::COLOR_TOOLBAR_STROKE :
-                   ThemeProperties::COLOR_TOOLBAR_STROKE_INACTIVE);
-  }
-  return themeProvider->GetNSColor(
-             ThemeProperties::COLOR_DETACHED_BOOKMARK_BAR_SEPARATOR);
-}
-
 - (NSPoint)patternPhase {
   // We want our backgrounds for the shelf to be phased from the upper
   // left hand corner of the view. Offset it by tab height so that the
@@ -55,17 +40,10 @@
 - (void)drawRect:(NSRect)dirtyRect {
   [super drawRect:dirtyRect];
 
-  // Draw top stroke
+  // Draw the top highlight
   NSRect borderRect, contentRect;
   NSDivideRect([self bounds], &borderRect, &contentRect, [self cr_lineWidth],
                NSMaxYEdge);
-  if (NSIntersectsRect(borderRect, dirtyRect)) {
-    [[self strokeColor] set];
-    NSRectFillUsingOperation(NSIntersectionRect(borderRect, dirtyRect),
-                             NSCompositeSourceOver);
-  }
-
-  // Draw the top highlight
   borderRect.origin.y -= [self cr_lineWidth];
   if (NSIntersectsRect(borderRect, dirtyRect)) {
     const ui::ThemeProvider* themeProvider = [[self window] themeProvider];