DevTools: do not update ui on every warning update.

Source/devtools/front_end/ResponsiveDesignView.js

Index: Source/devtools/front_end/ResponsiveDesignView.js
diff --git a/Source/devtools/front_end/ResponsiveDesignView.js b/Source/devtools/front_end/ResponsiveDesignView.js
index 4883275c38c87777eb39dbbb6a3acacaac5aa1ed..da221f4ebff4591127f0b2720abb1fa34027a88d 100644
--- a/Source/devtools/front_end/ResponsiveDesignView.js
+++ b/Source/devtools/front_end/ResponsiveDesignView.js
@@ -454,13 +454,15 @@ WebInspector.ResponsiveDesignView.prototype = {
         fieldsetElement.appendChild(WebInspector.SettingsUI.createSettingCheckbox(WebInspector.UIString("Viewport"), WebInspector.overridesSupport.settings.emulateViewport, true));
 
         // Warning
-        this._warningMessage = this._responsiveDesignContainer.element.createChild("div", "responsive-design-warning");
+        this._warningMessage = this._responsiveDesignContainer.element.createChild("div", "responsive-design-warning hidden");
         WebInspector.overridesSupport.addEventListener(WebInspector.OverridesSupport.Events.OverridesWarningUpdated, this._overridesWarningUpdated, this);
     },
 
     _overridesWarningUpdated: function()
     {
         var message = WebInspector.overridesSupport.warningMessage();
+        if (this._warningMessage.textContent === message)
+            return;
         this._warningMessage.classList.toggle("hidden", !message);
         this._warningMessage.textContent = message;
         this._responsiveDesignModeChanged();