Enable the dependency on google_toolbox_for_mac.

We converted this target to GN already, so app_list can depend on it as
is. This should address the TODO(GYP) in the BUILD.gn file.

BUG=None
TEST=None
R=brettw@chromium.org
TBR=xiyuan@chromium.org,mark@chromium.org

Review URL: https://codereview.chromium.org/590863002

Cr-Commit-Position: refs/heads/master@{#297123}

ui/app_list/BUILD.gn

@@ -168,7 +168,7 @@ component("app_list") {
       "cocoa/scroll_view_with_no_scrollbars.mm",
     ]
     deps += [
-      #"../../third_party/google_toolbox_for_mac/google_toolbox_for_mac.gyp:google_toolbox_for_mac",  TODO(GYP)
+      "//third_party/google_toolbox_for_mac",
     ]
     libs = [ "QuartzCore.framework" ]
   }