Support for css-color-4 (finish)

Issue #4

devtools/shared/fronts/css-properties.js

@@ -46,6 +46,20 @@ const CssPropertiesFront = FrontClassWithSpec(cssPropertiesSpec, {
   }
 });
 
+/**
+ * Query the feature supporting status in the featureSet.
+ *
+ * @param {Hashmap} featureSet the feature set hashmap
+ * @param {String} feature the feature name string
+ * @return {Boolean} has the feature or not
+ */
+function hasFeature(featureSet, feature) {
+  if (feature in featureSet) {
+    return featureSet[feature];
+  }
+  return false;
+}
+
 /**
  * Ask questions to a CSS database. This class does not care how the database
  * gets loaded in, only the questions that you can ask to it.
@@ -62,10 +76,16 @@ function CssProperties(db) {
   this.properties = db.properties;
   this.pseudoElements = db.pseudoElements;
 
+  // supported feature
+  this.cssColor4ColorFunction = hasFeature(db.supportedFeature,
+                                           "css-color-4-color-function");
+
   this.isKnown = this.isKnown.bind(this);
   this.isInherited = this.isInherited.bind(this);
   this.supportsType = this.supportsType.bind(this);
   this.isValidOnClient = this.isValidOnClient.bind(this);
+  this.supportsCssColor4ColorFunction =
+    this.supportsCssColor4ColorFunction.bind(this);
 
   // A weakly held dummy HTMLDivElement to test CSS properties on the client.
   this._dummyElements = new WeakMap();
@@ -181,6 +201,15 @@ CssProperties.prototype = {
     }
     return [];
   },
+
+  /**
+   * Checking for the css-color-4 color function support.
+   *
+   * @return {Boolean} Return true if the server supports css-color-4 color function.
+   */
+  supportsCssColor4ColorFunction() {
+    return this.cssColor4ColorFunction;
+  },
 };
 
 /**
@@ -292,6 +321,11 @@ function normalizeCssData(db) {
 
   reattachCssColorValues(db);
 
+  // If there is no supportedFeature in db, create an empty one.
+  if (!db.supportedFeature) {
+    db.supportedFeature = {};
+  }
+
   return db;
 }