Revert of Ensure BrowserThread::CurrentlyOn is correct through MessageLoop teardown

content/browser/browser_thread_impl.cc

Index: content/browser/browser_thread_impl.cc
diff --git a/content/browser/browser_thread_impl.cc b/content/browser/browser_thread_impl.cc
index cc5b9d00428c06c64e89675609321535fbc0e121..274acc39afe3e6f445b29aa6c29b74026b06461b 100644
--- a/content/browser/browser_thread_impl.cc
+++ b/content/browser/browser_thread_impl.cc
@@ -106,18 +106,13 @@
                                           "BrowserBlocking",
                                           base::TaskPriority::USER_VISIBLE)) {
     memset(threads, 0, BrowserThread::ID_COUNT * sizeof(threads[0]));
-    memset(thread_ids, 0, BrowserThread::ID_COUNT * sizeof(thread_ids[0]));
     memset(thread_delegates, 0,
            BrowserThread::ID_COUNT * sizeof(thread_delegates[0]));
   }
 
-  // This lock protects |threads| and |thread_ids|. Do not read or modify those
-  // arrays without holding this lock. Do not block while holding this lock.
+  // This lock protects |threads|. Do not read or modify that array
+  // without holding this lock. Do not block while holding this lock.
   base::Lock lock;
-
-  // This array is protected by |lock|. IDs in this array are populated as soon
-  // as their respective thread is started and are never reset.
-  base::PlatformThreadId thread_ids[BrowserThread::ID_COUNT];
 
   // This array is protected by |lock|. The threads are not owned by this
   // array. Typically, the threads are owned on the UI thread by
@@ -140,13 +135,6 @@
 BrowserThreadImpl::BrowserThreadImpl(ID identifier)
     : Thread(GetThreadName(identifier)), identifier_(identifier) {
   Initialize();
-
-  // Unit tests may create multiple TestBrowserThreadBundles, causing the same
-  // BrowserThread ID to be reinitialized. We explicitly clear the thread ID
-  // here so Start() can sanity check.
-  BrowserThreadGlobals& globals = g_globals.Get();
-  base::AutoLock lock(globals.lock);
-  globals.thread_ids[identifier] = base::kInvalidThreadId;
 }
 
 BrowserThreadImpl::BrowserThreadImpl(ID identifier,
@@ -154,12 +142,6 @@
     : Thread(GetThreadName(identifier)), identifier_(identifier) {
   set_message_loop(message_loop);
   Initialize();
-
-  // If constructed with an explicit message loop, this is a fake BrowserThread
-  // which runs on the current thread.
-  BrowserThreadGlobals& globals = g_globals.Get();
-  base::AutoLock lock(globals.lock);
-  globals.thread_ids[identifier] = base::PlatformThread::CurrentId();
 }
 
 // static
@@ -335,28 +317,15 @@
 #endif
 }
 
-bool BrowserThreadImpl::Start() {
-  return StartWithOptions(base::Thread::Options());
-}
-
 bool BrowserThreadImpl::StartWithOptions(const Options& options) {
   // The global thread table needs to be locked while a new thread is
   // starting, as the new thread can asynchronously start touching the
   // table (and other thread's message_loop).
   BrowserThreadGlobals& globals = g_globals.Get();
   base::AutoLock lock(globals.lock);
-  DCHECK_EQ(globals.thread_ids[identifier_], base::kInvalidThreadId);
-  bool result = Thread::StartWithOptions(options);
-  globals.thread_ids[identifier_] = GetThreadId();
-  return result;
-}
-
-bool BrowserThreadImpl::StartAndWaitForTesting() {
-  if (!Start())
-    return false;
-  WaitUntilThreadStarted();
-  return true;
-}
+  return Thread::StartWithOptions(options);
+}
+
 // static
 bool BrowserThreadImpl::PostTaskHelper(
     BrowserThread::ID identifier,
@@ -456,7 +425,9 @@
   base::AutoLock lock(globals.lock);
   DCHECK_GE(identifier, 0);
   DCHECK_LT(identifier, ID_COUNT);
-  return base::PlatformThread::CurrentId() == globals.thread_ids[identifier];
+  return globals.threads[identifier] &&
+         globals.threads[identifier]->message_loop() ==
+             base::MessageLoop::current();
 }
 
 // static