[Mac][Material Design] Fix SelectedKeywordDecoration tests for MD.

chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.mm

Index: chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.mm
diff --git a/chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.mm b/chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.mm
index eb64a73eece6b39a711c4a88e673e4a768ca7c1a..f0ef51cf3c826e244e52dd1ac08a65845e6c34ea 100644
--- a/chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.mm
+++ b/chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.mm
@@ -459,6 +459,10 @@ void LocationBarViewMac::Layout() {
     location_icon_decoration_->SetVisible(false);
     selected_keyword_decoration_->SetVisible(true);
     selected_keyword_decoration_->SetKeyword(short_name, is_extension_keyword);
+    // Note: the first time through this code path the
+    // |selected_keyword_decoration_| has no image set because under Material
+    // Design we need to set its color, which we cannot do until we know the
+    // theme (by being installed in a browser window).
     selected_keyword_decoration_->SetImage(GetKeywordImage(keyword));
   } else if (ShouldShowEVBubble()) {
     // Switch from location icon to show the EV bubble instead.