Remove disabling of C4267 in 64-bit gn builds

mash/quick_launch/quick_launch_application.cc

Index: mash/quick_launch/quick_launch_application.cc
diff --git a/mash/quick_launch/quick_launch_application.cc b/mash/quick_launch/quick_launch_application.cc
index f4ada352b255b57cbb5c3b75499082fcf0d8ea04..f10b77fe06bd527200406ea86268c63ecbdeb886 100644
--- a/mash/quick_launch/quick_launch_application.cc
+++ b/mash/quick_launch/quick_launch_application.cc
@@ -99,7 +99,8 @@ class QuickLaunchUI : public views::WidgetDelegateView,
         base::string16 suffix = name;
         base::ReplaceSubstringsAfterOffset(&suffix, 0, new_contents,
                                            base::string16());
-        gfx::Range range(new_contents.size(), name.size());
+        gfx::Range range(static_cast<uint32_t>(new_contents.size()),
+                         static_cast<uint32_t>(name.size()));
         prompt_->SetText(name);
         prompt_->SelectRange(range);
         break;