Write mojom and StructTraits for DisplaySnapshot.

ui/display/types/display_mode.cc

Index: ui/display/types/display_mode.cc
diff --git a/ui/display/types/display_mode.cc b/ui/display/types/display_mode.cc
index 6d43caa5638406c5e43a4b7003d0e491db066715..80f90c8685d2d96fa468310733eb4537eb2d2de9 100644
--- a/ui/display/types/display_mode.cc
+++ b/ui/display/types/display_mode.cc
@@ -24,6 +24,16 @@ std::unique_ptr<DisplayMode> DisplayMode::Clone() const {
                                           refresh_rate_));
 }
 
+bool DisplayMode::operator==(const DisplayMode& other) const {
+  return this->size() == display_mode.size() &&
+         this->is_interlaced() == display_mode.is_interlaced() &&
+         this->refresh_rate() == display_mode.refresh_rate();
+}
+
+bool DisplayMode::operator!=(const DisplayMode& other) const {
+  return !operator==(other);
+}
+
 std::string DisplayMode::ToString() const {
   return base::StringPrintf("[%dx%d %srate=%f]",
                             size_.width(),