Implement Puppeteer's setBlockedURLs method

This patch implements Puppeteer's Page.setBlockedURLs method.
This is a less agile alternative to the phantom's request.abort()
api.

This patch also adds a loadurlwithoutcss.js example re-implementation
to illustrate the usage of Page.setBlockedURLs.

examples/loadurlwithoutcss.js

@@ -0,0 +1,33 @@
+/**
+ * Copyright 2017 Google Inc., PhantomJS Authors All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+var Browser = require('../lib/Browser');
+
+if (process.argv.length < 3) {
+    console.log('Usage: loadurlwithoutcss.js URL');
+    return;
+}
+
+var address = process.argv[2];
+
+var browser = new Browser({headless: false});
+browser.newPage().then(async page => {
+    await page.setBlockedURLs(['*.css']);
+    var success = await page.navigate(address);
+    if (!success)
+        console.log('Unable to load the address!');
+//    browser.close();
+});

lib/Page.js

@@ -54,6 +54,8 @@ class Page extends EventEmitter {
         this._sourceURLToPageCallback = new Map();
         /** @type {!Map<string, !InPageCallback>} */
         this._scriptIdToPageCallback = new Map();
+        /** @type {!Array<string>} */
+        this._blockedURLs = [];
 
         client.on('Debugger.paused', event => this._onDebuggerPaused(event));
         client.on('Debugger.scriptParsed', event => this._onScriptParsed(event));
@@ -64,6 +66,17 @@ class Page extends EventEmitter {
         client.on('Runtime.exceptionThrown', exception => this._handleException(exception.exceptionDetails));
     }
 
+    /**
+     * @param {!Array<string>} patterns
+     * @return {!Promise}
+     */
+    async setBlockedURLs(patterns) {
+        this._blockedURLs = patterns;
+        await this._client.send('Network.setBlockedURLs', {
+            urls: patterns
+        });
+    }
+
     /**
      * @param {string} url
      * @return {!Promise}