Remove InterceptedRequest.isHandled() method

This patch removes the InterceptedRequest.isHandled method. There's
always a single request interceptor who owns all the intercepted
requests and who know if they were handled.

References #115.

docs/api.md

@@ -107,7 +107,6 @@
     + [interceptedRequest.abort()](#interceptedrequestabort)
     + [interceptedRequest.continue()](#interceptedrequestcontinue)
     + [interceptedRequest.headers](#interceptedrequestheaders)
-    + [interceptedRequest.isHandled()](#interceptedrequestishandled)
     + [interceptedRequest.method](#interceptedrequestmethod)
     + [interceptedRequest.postData](#interceptedrequestpostdata)
     + [interceptedRequest.url](#interceptedrequesturl)
@@ -969,9 +968,6 @@ Contains the [Headers] object associated with the request.
 Headers could be mutated with the `headers.append`, `headers.set` and other
 methods. Must not be changed in response to an authChallenge.
 
-#### interceptedRequest.isHandled()
-- returns: <[boolean]> returns `true` if either `abort` or `continue` was called on the object. Otherwise, returns `false`.
-
 #### interceptedRequest.method
 - <[string]>
 

lib/NetworkManager.js

@@ -369,13 +369,6 @@ class InterceptedRequest {
       headers: headers
     });
   }
-
-  /**
-   * @return {boolean}
-   */
-  isHandled() {
-    return this._handled;
-  }
 }
 
 NetworkManager.Events = {