Add support for multimedia timers to TaskQueue on Windows.

Multimedia timers are higher precision than WM_TIMER, but they're also
a limited resource and more costly. So this implementation is a best
effort implementation that falls back on WM_TIMER when multimedia
timers aren't available.

A possible future change could be to make high precision timers in a
TaskQueue, optional. The reason for doing so would be for TaskQueues
that don't need high precision timers, won't eat up timers from TQ
instances that really need it.

BUG=webrtc:7151

Review-Url: https://codereview.webrtc.org/2691973002
Cr-Commit-Position: refs/heads/master@{#16661}
diff --git a/webrtc/base/task_queue_unittest.cc b/webrtc/base/task_queue_unittest.cc
index 08123d0..74433b9 100644
--- a/webrtc/base/task_queue_unittest.cc
+++ b/webrtc/base/task_queue_unittest.cc
@@ -112,14 +112,14 @@
   TaskQueue queue(kQueueName);
 
   std::vector<std::unique_ptr<Event>> events;
-  for (int i = 0; i < 10; ++i) {
+  for (int i = 0; i < 100; ++i) {
     events.push_back(std::unique_ptr<Event>(new Event(false, false)));
     queue.PostDelayedTask(
         Bind(&CheckCurrent, kQueueName, events.back().get(), &queue), 10);
   }
 
   for (const auto& e : events)
-    EXPECT_TRUE(e->Wait(100));
+    EXPECT_TRUE(e->Wait(1000));
 }
 
 TEST(TaskQueueTest, PostDelayedAfterDestruct) {