Devtools: [WIP] Implement enhanced devtools extension language APIs

Source/devtools/front_end/sources/WatchExpressionsSidebarPane.js

Index: Source/devtools/front_end/sources/WatchExpressionsSidebarPane.js
diff --git a/Source/devtools/front_end/sources/WatchExpressionsSidebarPane.js b/Source/devtools/front_end/sources/WatchExpressionsSidebarPane.js
index 581d01f5f2e924e51870f33b4977cdd79432582f..b651b47e6a5c8beb9279c29305f4508086605538 100644
--- a/Source/devtools/front_end/sources/WatchExpressionsSidebarPane.js
+++ b/Source/devtools/front_end/sources/WatchExpressionsSidebarPane.js
@@ -254,8 +254,26 @@ WebInspector.WatchExpression.prototype = {
     update: function()
     {
         var currentExecutionContext = WebInspector.context.flavor(WebInspector.ExecutionContext);
-        if (currentExecutionContext && this._expression)
+        if (currentExecutionContext && this._expression) {
+            var location = currentExecutionContext.pauseLocation();
+            if (location) {
+                var activeMime = WebInspector.ResourceType.mimeFromUrl(location.source);
+                if (WebInspector.languageService.handles.transpile(activeMime)) {
+                    var expr = this._expression;
+                    var prom = this._pendingUpdate = WebInspector.languageService.transpile(activeMime, expr, location).then(result => {
+                        if (this._pendingUpdate !== prom) {
+                            //cancelled by another update
+                            return;
+                        }
+                        currentExecutionContext.evaluate(result, WebInspector.WatchExpression._watchObjectGroupId, false, true, false, false, this._createWatchExpression.bind(this));
+                    }).catch((e) => {
+                        currentExecutionContext.evaluate(expr, WebInspector.WatchExpression._watchObjectGroupId, false, true, false, false, this._createWatchExpression.bind(this));
+                    });
+                    return;
+                }
+            }
             currentExecutionContext.evaluate(this._expression, WebInspector.WatchExpression._watchObjectGroupId, false, true, false, false, this._createWatchExpression.bind(this));
+        }
     },
 
     startEditing: function()