Adds a flag to support "Virtual Time" to the blink scheduler

components/scheduler/BUILD.gn

Index: components/scheduler/BUILD.gn
diff --git a/components/scheduler/BUILD.gn b/components/scheduler/BUILD.gn
index 8065258cf826f7596e7b4a929d2619cc2c98d8c7..fa3b826f69d8b6295dac4fb19e8ff5bad6473859 100644
--- a/components/scheduler/BUILD.gn
+++ b/components/scheduler/BUILD.gn
@@ -16,6 +16,7 @@ component("scheduler") {
   configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]
 
   deps = [
+    ":common",
     "//base",
     "//cc:cc",
     "//third_party/WebKit/public:blink",
@@ -27,6 +28,13 @@ component("scheduler") {
   ]
 }
 
+# GYP version: components/scheduler.gypi:scheduler_common
+source_set("common") {
+  sources = rebase_path(scheduler_gypi_values.scheduler_common_sources,
+                        ".",
+                        "//components/scheduler")
+}
+
 source_set("unit_tests") {
   testonly = true
 
@@ -45,6 +53,7 @@ source_set("unit_tests") {
     "child/scheduler_task_runner_delegate_for_test.cc",
     "child/scheduler_task_runner_delegate_for_test.h",
     "child/scheduler_task_runner_delegate_impl_unittest.cc",
+    "child/virtual_time_task_runner_delegate_unittest.cc",
     "child/webthread_impl_for_worker_scheduler_unittest.cc",
     "child/worker_scheduler_impl_unittest.cc",
     "renderer/deadline_task_runner_unittest.cc",