Fix all strong-mode errors and warnings.

lib/src/frontend/timeout.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:string_scanner/string_scanner.dart';
 
 /// A regular expression that matches text until a letter or whitespace.
 ///
 /// This is intended to scan through a number without actually encoding the full
 /// Dart number grammar. It doesn't stop on "e" because that can be a component
@@ skipping 71 matching lines @@
     var number = double.parse(scanner.lastMatch[0]);
 
     // A number followed by "x" is a scale factor.
     if (scanner.scan("x") || scanner.scan("X")) {
       scanner.expectDone();
       return new Timeout.factor(number);
     }
 
     // Parse time units until none are left. The condition is in the middle of
     // the loop because we've already parsed the first number.
-    var microseconds = 0;
+    var microseconds = 0.0;
     while (true) {
       scanner.expect(_unit, name: "unit");
       microseconds += _microsecondsFor(number, scanner.lastMatch[0]);
 
       scanner.scan(_whitespace);
 
       // Scan the next number, if it's avaialble.
       if (!scanner.scan(_untilUnit)) break;
       number = double.parse(scanner.lastMatch[0]);
     }
@@ skipping 40 matching lines @@
 
   bool operator==(other) => other is Timeout && other.duration == duration &&
       other.scaleFactor == scaleFactor;
 
   String toString() {
     if (duration != null) return duration.toString();
     if (scaleFactor != null) return "${scaleFactor}x";
     return "none";
   }
 }