[Mac][Material Design] Update Omnibox dropdown on Mac to MD

chrome/browser/ui/cocoa/omnibox/omnibox_popup_separator_view.mm

Index: chrome/browser/ui/cocoa/omnibox/omnibox_popup_separator_view.mm
diff --git a/chrome/browser/ui/cocoa/omnibox/omnibox_popup_separator_view.mm b/chrome/browser/ui/cocoa/omnibox/omnibox_popup_separator_view.mm
index 49f9a0df1fa639660a01f6adf533dd1ff55a50dd..b981d7dda9ae2b14825791666b291913e66f7b86 100644
--- a/chrome/browser/ui/cocoa/omnibox/omnibox_popup_separator_view.mm
+++ b/chrome/browser/ui/cocoa/omnibox/omnibox_popup_separator_view.mm
@@ -4,6 +4,7 @@
 
 #import "chrome/browser/ui/cocoa/omnibox/omnibox_popup_separator_view.h"
 
+#import "base/mac/scoped_nsobject.h"
 #include "grit/theme_resources.h"
 #import "ui/base/cocoa/nsview_additions.h"
 #include "ui/base/resource/resource_bundle.h"
@@ -32,11 +33,40 @@
   return [shadowImage size].height;
 }
 
+- (instancetype)initWithFrame:(NSRect)frame forDarkTheme:(BOOL)isDarkTheme {
+  if ((self = [self initWithFrame:frame])) {
+    isDarkTheme_ = isDarkTheme;
+    // For dark themes the OmniboxPopupBottomSeparatorView will render a shadow
+    // rather than blit a bitmap. Shadows are expensive to draw so use a layer
+    // to cache the result.
+    if (isDarkTheme_) {
+      [self setWantsLayer:YES];
+    }
+  }
+  return self;
+}
+
 - (void)drawRect:(NSRect)rect {
-  ResourceBundle& rb = ResourceBundle::GetSharedInstance();
   NSRect bounds = [self bounds];
 
+  if (isDarkTheme_) {
+    // There's an image for the shadow the Omnibox casts, but this shadow is
+    // an opaque mix of white and black, which makes it look strange against a
+    // dark NTP page. For dark mode, draw the shadow in code instead so that
+    // it has some transparency.
+    base::scoped_nsobject<NSShadow> shadow([[NSShadow alloc] init]);
+    [shadow setShadowBlurRadius:8];
+    [shadow setShadowColor:[NSColor blackColor]];
+    [shadow set];
+
+    // Fill a rect that's out of view to get just the shadow it casts.
+    [[NSColor blackColor] set];
+    NSRectFill(NSMakeRect(-3, NSMaxY(bounds), NSWidth(bounds) + 6, 5));
+    return;
+  }
+
   // Draw the shadow.
+  ResourceBundle& rb = ResourceBundle::GetSharedInstance();
   NSImage* shadowImage =
       rb.GetNativeImageNamed(IDR_OVERLAY_DROP_SHADOW).ToNSImage();
   [shadowImage drawInRect:bounds