Added TestRunner.Session.createTargetInNewContext helper method

Change-Id: I684ca08b91cfc997f38018191d4963eaa8a06d25
Reviewed-on: https://chromium-review.googlesource.com/1130553
Commit-Queue: Peter Kvitek <kvitekp@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573835}

third_party/WebKit/LayoutTests/http/tests/inspector-protocol/resources/inspector-protocol-test.js

@@ -264,6 +264,17 @@ TestRunner.Session = class {
     return session;
   }
 
+  async createTargetInNewContext(width, height, url, enableBeginFrameControl) {
+    const browserContextId = (await this.protocol.Target.createBrowserContext())
+        .result.browserContextId;
+    const targetId = (await this.protocol.Target.createTarget(
+        {url, browserContextId, width, height, enableBeginFrameControl}))
+        .result.targetId;
+    const sessionId = (await this.protocol.Target.attachToTarget({targetId}))
+        .result.sessionId;
+    return this.createChild(sessionId);
+  }
+
   _dispatchMessageFromTarget(event) {
     var session = this._childSessions.get(event.params.sessionId);
     if (session)