Making it possible to import mediastream tests.

LayoutTests/resources/vendor-prefix.js

+/* Use this script when you want to test APIs that use vendor prefixes
+   and define which objects need to be checked for prefixed versions, à la
+   <script src="vendor-prefix.js"
+     data-prefixed-objects='[{"ancestors":["navigator"], "name":"getUserMedia"}]'
+   data-prefixed-prototypes='[{"ancestors":["HTMLMediaElement"],"name":"srcObject"}]'></script>
+   data-prefixed-objects lets prefix objects in the global space
+   data-prefixed-prototypes adds prefixes to interfaces, for objects that
+   get created during the tests
+
+   NB: vendor prefixes are expected to go away in favor of putting
+   new features behind flag, so hopefully there will be only limited
+   need to use this
+*/
+
+(function () {
+    var aliases = {};
+    var documentingPrefixUsage = document.createElement('div');
+    var vendorPrefixes = ["moz", "ms", "o", "webkit", "Moz", "MS", "O", "WebKit", "op"];
+
+    function getParentObject(ancestors) {
+        var parent = window;
+        var currentName = "";
+        ancestors.forEach(function (p) {
+            currentName = currentName ? currentName + "." + p : p;
+            if (parent[p] === undefined) {
+                throw currentName + " is undefined, cannot set prefix alias on child object";
+            }
+            parent = parent[p];
+        });
+        return parent;
+    }
+
+    function prependPrefix(prefix, name) {
+        var newName = name[0].toUpperCase() + name.substr(1, name.length);
+        return prefix + newName;
+    }
+
+    function setPrototypeAlias(obj) {
+        var parent = getParentObject(obj.ancestors);
+        if (!parent.prototype.hasOwnProperty(obj.name)) {
+            vendorPrefixes.forEach(function (prefix) {
+                if (parent.prototype.hasOwnProperty(prependPrefix(prefix, obj.name))) {
+                    Object.defineProperty(parent.prototype, obj.name,
+                                          {get: function() {return this[prependPrefix(prefix, obj.name)];},
+                                           set: function(v) {this[prependPrefix(prefix, obj.name)] = v;}
+                                          });
+                    aliases[obj.ancestors.join(".") + ".prototype." + obj.name] = obj.ancestors.join(".") + ".prototype." + prependPrefix(prefix, obj.name);
+                    return;
+                }
+            });
+        }
+    }
+
+    function setAlias(obj) {
+        var parent = getParentObject(obj.ancestors);
+        if (parent[obj.name] === undefined) {
+            vendorPrefixes.forEach(function (prefix) {
+                if (parent[prependPrefix(prefix, obj.name)] !== undefined) {
+                    parent[obj.name] = parent[prependPrefix(prefix, obj.name)];
+                    aliases[obj.ancestors.join(".") + "." + obj.name] = obj.ancestors.join(".") + "." + prependPrefix(prefix, obj.name);
+                    return;
+                }
+            });
+        }
+    }
+
+    // For this version of vendor-prefixes.js, always replace the prefixes.
+    if (document.querySelector("script[data-prefixed-objects]")) {
+        var prefixObjectsData = document.querySelector("script[data-prefixed-objects]").dataset["prefixedObjects"];
+        try {
+            var prefixedObjects = JSON.parse(prefixObjectsData);
+        } catch (e) {
+            throw "couldn't parse data-prefixed-objects as JSON:" + e;
+        }
+        prefixedObjects.forEach(setAlias);
+    }
+    if (document.querySelector("script[data-prefixed-prototypes]")) {
+        var prefixProtoData = document.querySelector("script[data-prefixed-prototypes]").dataset["prefixedPrototypes"];
+        try {
+            var prefixedPrototypes = JSON.parse(prefixProtoData);
+        } catch (e) {
+            throw "couldn't parse data-prefixed-prototypes as JSON:" + e;
+        }
+        prefixedPrototypes.forEach(setPrototypeAlias);
+    }
+})();