Experiment with redirecting all BrowserThreads (but UI/IO) to TaskScheduler

content/public/test/test_browser_thread.cc

Index: content/public/test/test_browser_thread.cc
diff --git a/content/public/test/test_browser_thread.cc b/content/public/test/test_browser_thread.cc
index ae83f78f78aad1455f8a9f98aa6c4f003ef4499b..54db8953941918246ff1cecda725c13340a1ca65 100644
--- a/content/public/test/test_browser_thread.cc
+++ b/content/public/test/test_browser_thread.cc
@@ -40,15 +40,34 @@ class TestBrowserThreadImpl : public BrowserThreadImpl {
 };
 
 TestBrowserThread::TestBrowserThread(BrowserThread::ID identifier)
-    : impl_(new TestBrowserThreadImpl(identifier)) {
-}
+    : impl_(new TestBrowserThreadImpl(identifier)), identifier_(identifier) {}
 
 TestBrowserThread::TestBrowserThread(BrowserThread::ID identifier,
                                      base::MessageLoop* message_loop)
-    : impl_(new TestBrowserThreadImpl(identifier, message_loop)) {}
+    : impl_(new TestBrowserThreadImpl(identifier, message_loop)),
+      identifier_(identifier) {}
 
 TestBrowserThread::~TestBrowserThread() {
-  Stop();
+  // The upcoming BrowserThreadImpl::ResetGlobalsForTesting() call requires that
+  // |impl_| have triggered the shutdown phase for its BrowserThread::ID. This
+  // either happens when the thread is stopped (if real) or destroyed (when fake
+  // -- i.e. using an externally provided MessageLoop).
+  impl_.reset();
+
+  // Resets BrowserThreadImpl's globals so that |impl_| is no longer bound to
+  // |identifier_|. This is fine since the underlying MessageLoop has already
+  // been flushed and deleted in Stop(). In the case of an externally provided
+  // MessageLoop however, this means that TaskRunners obtained through
+  // |BrowserThreadImpl::GetTaskRunnerForThread(identifier_)| will no longer
+  // recognize their BrowserThreadImpl for RunsTasksOnCurrentThread(). This
+  // happens most often when such verifications are made from
+  // MessageLoop::DestructionObservers. Callers that care to work around that
+  // should instead use this shutdown sequence:
+  //   1) TestBrowserThread::Stop()
+  //   2) ~MessageLoop()
+  //   3) ~TestBrowserThread()
+  // (~TestBrowserThreadBundle() does this).
+  BrowserThreadImpl::ResetGlobalsForTesting(identifier_);
 }
 
 bool TestBrowserThread::Start() {