fix(page): execute frame.waitFor{Selector,XPath} in secondary world (#3856)

This patch starts executing frame.waitForSelector and frame.waitForXPath
in secondary world. As a result, websites that mutate page global
context (e.g. removing global MutationObserver) don't break Puppeteer's
behavior.

Fixes #609

lib/ExecutionContext.js

@@ -173,6 +173,22 @@ class ExecutionContext {
     });
     return createJSHandle(this, response.objects);
   }
+
+  /**
+   * @param {Puppeteer.ElementHandle} elementHandle
+   * @return {Promise<Puppeteer.ElementHandle>}
+   */
+  async _adoptElementHandle(elementHandle) {
+    assert(elementHandle.executionContext() !== this, 'Cannot adopt handle that already belongs to this execution context');
+    assert(this._world, 'Cannot adopt handle without DOMWorld');
+    const nodeInfo = await this._client.send('DOM.describeNode', {
+      objectId: elementHandle._remoteObject.objectId,
+    });
+    const {object} = await this._client.send('DOM.resolveNode', {
+      backendNodeId: nodeInfo.node.backendNodeId,
+    });
+    return /** @type {Puppeteer.ElementHandle}*/(createJSHandle(this, object));
+  }
 }
 
 module.exports = {ExecutionContext, EVALUATION_SCRIPT_URL};