Replace FakeStopwatch with Clock.newStopwatch

[seaneagan]

Time-dependent units can receive Clocks as dependencies to mock the passage of time. Doing so exposes nothing about their implementation, only that they depend on the passage of time. #98 removed the need to expose the use of Timers. This issue is to remove the need to expose the use of Stopwatches. Currently quiver has FakeStopwatch for mocking stopwatches. Receiving a Stopwatch (FakeStopwatch) as a dependency, exposes even more of the implementation, specifically that you're using only a single stopwatch. A StopwatchFactory typedef would at least solve that, but it still would expose the use of Stopwatches.

If it were possible to obtain a Stopwatch from a Clock, the time-dependen unit could then just receive a Clock, and create the Stopwatch internally.

Ideally the dart:core Stopwatch impl would be backed by a Clock, see:

https://code.google.com/p/dart/issues/detail?id=18149

But until then, we will want to use the dart:core stopwatch impl in production code, and a clock-backed Stopwatch in test code. The way to handle this is polymorphism, by adding a stopwatch creation method to Clock:

Stopwatch newStopwatch();

createStopwatch could also work as a name.

It should be a method instead of a getter, since it returns a new mutable object on each invocation.

[trinarytree]

Minor problem: FakeStopwatch currently is in the testing directory but Clock isn't, and most people probably don't want test code in production. Presumably, createStopwatch would create a FakeStopwatch. Part of the problem may be that FakeStopwatch has a prejudicial name. Like Clock, nothing is really "fake" about it, it's just driven by the now function it's given.

So maybe this would be a natural migration path:

• Rename FakeStopwatch to something more neutral-sounding, like DelegatingStopwatch.
• Move it closer to Clock so that it doesn't look like test-only code.
• Add Stopwatch createStopwatch() to Clock.

[tolotrasamuel]

Is quiver not maintained anymore ? What is the outcome of this issue ?