Add support for 'display-mode' MQ defined in Manifest spec

Source/core/css/MediaValuesCached.h

Index: Source/core/css/MediaValuesCached.h
diff --git a/Source/core/css/MediaValuesCached.h b/Source/core/css/MediaValuesCached.h
index 4a79e08c59b5680bd734a4d266ffbc306923df22..62d9b0f48da82e222db0bfbddfa773c005866f7f 100644
--- a/Source/core/css/MediaValuesCached.h
+++ b/Source/core/css/MediaValuesCached.h
@@ -28,6 +28,7 @@ public:
         bool threeDEnabled;
         bool strictMode;
         String mediaType;
+        DisplayMode displayMode;
 
         MediaValuesCachedData()
             : viewportWidth(0)
@@ -44,6 +45,7 @@ public:
             , defaultFontSize(16)
             , threeDEnabled(false)
             , strictMode(true)
+            , displayMode(DisplayModeBrowser)
         {
         }
     };
@@ -73,6 +75,7 @@ public:
     virtual Document* document() const override;
     virtual bool hasValues() const override;
     virtual const String mediaType() const override;
+    virtual DisplayMode displayMode() const override;
 
 protected:
     MediaValuesCached();