Make nesting/running states a RunLoop rather than a MessageLoop concept.

third_party/WebKit/Source/platform/scheduler/test/lazy_scheduler_message_loop_delegate_for_tests.cc

Index: third_party/WebKit/Source/platform/scheduler/test/lazy_scheduler_message_loop_delegate_for_tests.cc
diff --git a/third_party/WebKit/Source/platform/scheduler/test/lazy_scheduler_message_loop_delegate_for_tests.cc b/third_party/WebKit/Source/platform/scheduler/test/lazy_scheduler_message_loop_delegate_for_tests.cc
index bd41c59fef331ffed136343a1e3a45d4f71680ac..2dd45a83ad98f301b09236437bd9a904c2e6aac8 100644
--- a/third_party/WebKit/Source/platform/scheduler/test/lazy_scheduler_message_loop_delegate_for_tests.cc
+++ b/third_party/WebKit/Source/platform/scheduler/test/lazy_scheduler_message_loop_delegate_for_tests.cc
@@ -7,6 +7,7 @@
 #include <utility>
 
 #include "base/memory/ptr_util.h"
+#include "base/message_loop/message_loop.h"
 #include "base/time/default_tick_clock.h"
 
 namespace blink {
@@ -44,7 +45,7 @@ base::MessageLoop* LazySchedulerMessageLoopDelegateForTests::EnsureMessageLoop()
   if (pending_task_runner_)
     message_loop_->SetTaskRunner(std::move(pending_task_runner_));
   if (pending_observer_)
-    message_loop_->AddNestingObserver(pending_observer_);
+    base::RunLoop::AddNestingObserverOnCurrentThread(pending_observer_);
   return message_loop_;
 }
 
@@ -90,26 +91,51 @@ bool LazySchedulerMessageLoopDelegateForTests::RunsTasksOnCurrentThread()
 }
 
 bool LazySchedulerMessageLoopDelegateForTests::IsNested() const {
-  return EnsureMessageLoop()->IsNested();
+  DCHECK(RunsTasksOnCurrentThread());
+  EnsureMessageLoop();
+  return base::RunLoop::IsNestedOnCurrentThread();
 }
 
 void LazySchedulerMessageLoopDelegateForTests::AddNestingObserver(
-    base::MessageLoop::NestingObserver* observer) {
+    base::RunLoop::NestingObserver* observer) {
+  // While |observer| _could_ be associated with the current thread regardless
+  // of the presence of a MessageLoop, the association is delayed until
+  // EnsureMessageLoop() is invoked. This works around a state issue where
+  // otherwise many tests fail because of the following sequence:
+  //   1) blink::scheduler::CreateRendererSchedulerForTests()
+  //       -> TaskQueueManager::TaskQueueManager()
+  //       -> LazySchedulerMessageLoopDelegateForTests::AddNestingObserver()
+  //   2) Any test framework with a base::MessageLoop member (and not caring
+  //      about the blink scheduler) does:
+  //        ThreadTaskRunnerHandle::Get()->PostTask(
+  //            FROM_HERE, an_init_task_with_a_nested_loop);
+  //        RunLoop.RunUntilIdle();
+  //   3) |a_task_with_a_nested_loop| triggers
+  //          TaskQueueManager::OnBeginNestedLoop() which:
+  //            a) flags any_thread().is_nested = true;
+  //            b) posts a task to self, which triggers:
+  //                 LazySchedulerMessageLoopDelegateForTests::PostDelayedTask()
+  //   4) This self-task in turn triggers TaskQueueManager::DoWork()
+  //      which expects to be the only one to trigger nested loops (doesn't
+  //      support TaskQueueManager::OnBeginNestedLoop() being invoked before
+  //      it kicks in), resulting in it hitting:
+  //      DCHECK_EQ(any_thread().is_nested, delegate_->IsNested()); (1 vs 0).
+  // TODO(skyostil): fix this convulotion as part of http://crbug.com/495659.
   if (!HasMessageLoop()) {
     pending_observer_ = observer;
     return;
   }
-  message_loop_->AddNestingObserver(observer);
+  base::RunLoop::AddNestingObserverOnCurrentThread(observer);
 }
 
 void LazySchedulerMessageLoopDelegateForTests::RemoveNestingObserver(
-    base::MessageLoop::NestingObserver* observer) {
+    base::RunLoop::NestingObserver* observer) {
   if (!message_loop_ || message_loop_ != base::MessageLoop::current()) {
     DCHECK_EQ(pending_observer_, observer);
     pending_observer_ = nullptr;
     return;
   }
-  message_loop_->RemoveNestingObserver(observer);
+  base::RunLoop::RemoveNestingObserverOnCurrentThread(observer);
 }
 
 base::TimeTicks LazySchedulerMessageLoopDelegateForTests::NowTicks() {