i18n: add i18n for LighthouseError messages

lighthouse-core/gather/gather-runner.js

@@ -161,13 +161,13 @@ class GatherRunner {
       } else {
         return new LHError(
           LHError.errors.FAILED_DOCUMENT_REQUEST,
-          {errorDetails: `${netErr}`}
+          {errorDetails: netErr}
         );
       }
     } else if (mainRecord.hasErrorStatusCode()) {
       return new LHError(
         LHError.errors.ERRORED_DOCUMENT_REQUEST,
-        {statusCode: `${mainRecord.statusCode}`}
+        {statusCode: mainRecord.statusCode.toString()}
       );
     }
   }
@@ -184,7 +184,7 @@ class GatherRunner {
         .map(exp => exp.description);
       throw new LHError(
         LHError.errors.INSECURE_DOCUMENT_REQUEST,
-        {securityMessages: `${insecureDescriptions.join(' ')}`}
+        {securityMessages: insecureDescriptions.join(' ')}
       );
     }
   }

lighthouse-core/test/runner-test.js

@@ -625,8 +625,8 @@ describe('Runner', () => {
       assert.fail('should have thrown');
     } catch (err) {
       assert.equal(err.code, LHError.errors.PROTOCOL_TIMEOUT.code);
-      assert.ok(/^Waiting for DevTools protocol.*Method: Method.Failure/.test(err.friendlyMessage),
-        'should have prevented run');
+      /* eslint-disable-next-line max-len */
+      expect(err.friendlyMessage).toBeDisplayString('Waiting for DevTools protocol response has exceeded the allotted time. Method: Method.Failure.');
     }
   });