DevTools: Add support for adding folders to workspace with drag and drop (renderer part)

Source/devtools/front_end/externs.js

Index: Source/devtools/front_end/externs.js
diff --git a/Source/devtools/front_end/externs.js b/Source/devtools/front_end/externs.js
index 66c17e08dcd81d7f3fd30280a5ea64d7601a3ef4..c45204d30c181d251726a1fe61a30e73af48592b 100644
--- a/Source/devtools/front_end/externs.js
+++ b/Source/devtools/front_end/externs.js
@@ -195,6 +195,17 @@ function DOMFileSystem() {}
  */
 DOMFileSystem.prototype.root = null;
 
+// Drag and drop API
+/**
+ * @constructor
+ */
+function DataTransferItem() {}
+
+/**
+ * @return {Entry}
+ */
+DataTransferItem.prototype.webkitGetAsEntry = function() {}
+
 /** @type {Node} */
 Range.prototype.startContainer;
 
@@ -233,6 +244,7 @@ InspectorFrontendHostAPI.prototype.closeWindow = function() {}
 InspectorFrontendHostAPI.prototype.copyText = function(text) {}
 InspectorFrontendHostAPI.prototype.inspectedURLChanged = function(url) {}
 InspectorFrontendHostAPI.prototype.isolatedFileSystem = function(fileSystemId, registeredName) {}
+InspectorFrontendHostAPI.prototype.upgradeDraggedFileSystemPermissions = function(DOMFileSystem) {}
 InspectorFrontendHostAPI.prototype.loaded = function() {}
 InspectorFrontendHostAPI.prototype.localizedStringsURL = function() {}
 InspectorFrontendHostAPI.prototype.platform = function() {}