chore: stop using console.assert everywhere (#2646)

Since Node 10, `console.assert` no longer throws an AssertionError.
(This is generally good since it aligns Node.js with Browsers.)

This patch migrates all usages of `console.assert` in our codebase.
- All the `lib/` and testing code is migrated onto a handmade `assert`
function. This is to make Puppeteer transpilation / bundling easier.
- All the tooling is switched to use Node's `assert` module.

Fixes #2547.

lib/Connection.js

@@ -13,7 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-const {helper} = require('./helper');
+const {helper, assert} = require('./helper');
 const debugProtocol = require('debug')('puppeteer:protocol');
 const debugSession = require('debug')('puppeteer:session');
 
@@ -228,7 +228,7 @@ class CDPSession extends EventEmitter {
           this._sessions.delete(object.params.sessionId);
         }
       }
-      console.assert(!object.id);
+      assert(!object.id);
       this.emit(object.method, object.params);
     }
   }