New features include;
 * Actually running the tasks in the ordered you asked!
 * Allow running only pending tasks, all tasks until idle, to a given time or
   for a given period.
 * Allow stopping of running tasks on *any* arbitrary condition. No longer will
   your tasks stop working when someone adds a new task or changes the task
   order!
 * Task runner intimately connected to time and controls Now().
   Supports both automatic management and manual control.

This change makes it possible for the scheduler_unit tests to be 100%
deterministic. It also allows them to be more flexible and less brittle.

BUG=380889

Review URL: https://codereview.chromium.org/387493002

Cr-Commit-Position: refs/heads/master@{#294059}

diff --git a/cc/BUILD.gn b/cc/BUILD.gn
index 4222804..300150f 100644
--- a/cc/BUILD.gn
+++ b/cc/BUILD.gn

@@ -599,6 +599,8 @@
     "test/test_context_support.h",
     "test/test_gles2_interface.cc",
     "test/test_gles2_interface.h",
+    "test/test_now_source.cc",
+    "test/test_now_source.h",
     "test/test_occlusion_tracker.h",
     "test/test_shared_bitmap_manager.cc",
     "test/test_shared_bitmap_manager.h",