Implement Page.uploadFile (#61)

This patch implements `Page.uploadFile` method to support file upload inputs.

lib/NetworkManager.js

@@ -108,7 +108,10 @@ class NetworkManager extends EventEmitter {
    * @param {!Object} event
    */
   _onResponseReceived(event) {
-    let request = this._idToRequest.get(event.requestId) || null;
+    let request = this._idToRequest.get(event.requestId);
+    // FileUpload sends a response without a matching request.
+    if (!request)
+      return;
     let response = new Response(request, event.response, this._getResponseBody.bind(this, event.requestId));
     request._response = response;
     this.emit(NetworkManager.Events.Response, response);

lib/Page.js

@@ -493,10 +493,13 @@ class Page extends EventEmitter {
    * @param {!Promise<number>}
    */
   async _querySelector(selector) {
-    return (await this._client.send('DOM.querySelector', {
+    let {nodeId} = await this._client.send('DOM.querySelector', {
       nodeId: await this._rootNodeId(),
       selector
-    })).nodeId;
+    });
+    if (!nodeId)
+      throw new Error('No node found for selector: ' + selector);
+    return nodeId;
   }
 
   /**
@@ -569,6 +572,18 @@ class Page extends EventEmitter {
   waitFor(selector) {
     return this.mainFrame().waitFor(selector);
   }
+
+  /**
+   * @param {string} selector
+   * @param {!Array<string>} filePaths
+   * @return {!Promise}
+   */
+  async uploadFile(selector, ...filePaths) {
+    await this._client.send('DOM.setFileInputFiles', {
+      nodeId: await this._querySelector(selector),
+      files: filePaths
+    });
+  }
 }
 
 /** @enum {string} */