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};

lib/FrameManager.js

@@ -608,8 +608,14 @@ class Frame {
    * @param {!{visible?: boolean, hidden?: boolean, timeout?: number}=} options
    * @return {!Promise<?Puppeteer.ElementHandle>}
    */
-  waitForSelector(selector, options) {
-    return this._mainWorld.waitForSelector(selector, options);
+  async waitForSelector(selector, options) {
+    const handle = await this._secondaryWorld.waitForSelector(selector, options);
+    if (!handle)
+      return null;
+    const mainExecutionContext = await this._mainWorld.executionContext();
+    const result = await mainExecutionContext._adoptElementHandle(handle);
+    await handle.dispose();
+    return result;
   }
 
   /**
@@ -617,8 +623,14 @@ class Frame {
    * @param {!{visible?: boolean, hidden?: boolean, timeout?: number}=} options
    * @return {!Promise<?Puppeteer.ElementHandle>}
    */
-  waitForXPath(xpath, options) {
-    return this._mainWorld.waitForXPath(xpath, options);
+  async waitForXPath(xpath, options) {
+    const handle = await this._secondaryWorld.waitForXPath(xpath, options);
+    if (!handle)
+      return null;
+    const mainExecutionContext = await this._mainWorld.executionContext();
+    const result = await mainExecutionContext._adoptElementHandle(handle);
+    await handle.dispose();
+    return result;
   }
 
   /**