Fold IPCSupportInitializer::ForceShutdown() with ShutDown().

A race is possible on browser shut down where the UI thread releases
its last |ScopedIPCSupport| which then causes ShutDown() to call
ForceShutdown() since the last reference is released. However, at the
point ForceShutdown() is called, |lock_| is not held and so a utility
process being created on the IO thead can call Init() and assume it has
a reference to the IPC support. However, |shutting_down_| hasn't been
set yet, so there's no way to cancel the shutdown process. This causes
|ChannelManager| internally to post a task to the IO thread with a
reference to itself, even though it is about to be destroyed.

BUG=542069

Review URL: https://codereview.chromium.org/1412733006

Cr-Commit-Position: refs/heads/master@{#354924}

2 files changed, 13 insertions, 22 deletions

diff --git a/ipc/mojo/OWNERS b/ipc/mojo/OWNERS
index 584a1f6..ae47a47 100644
--- a/ipc/mojo/OWNERS
+++ b/ipc/mojo/OWNERS
@@ -1,2 +1,4 @@
+amistry@chromium.org
 morrita@chromium.org
-viettrungluu@chromium.org
\ No newline at end of file
+rockot@chromium.org
+viettrungluu@chromium.org
diff --git a/ipc/mojo/scoped_ipc_support.cc b/ipc/mojo/scoped_ipc_support.cc
index 5729463..2465aa2 100644
--- a/ipc/mojo/scoped_ipc_support.cc
+++ b/ipc/mojo/scoped_ipc_support.cc
@@ -31,10 +31,7 @@ class IPCSupportInitializer : public mojo::embedder::ProcessDelegate {
   ~IPCSupportInitializer() override { DCHECK(!observer_); }
 
   void Init(scoped_refptr<base::TaskRunner> io_thread_task_runner);
-  void ShutDown();
-
-  // Forces the initializer to shut down even if scopers are still holding it.
-  void ForceShutdown();
+  void ShutDown(bool force);
 
  private:
   // This watches for destruction of the MessageLoop that IPCSupportInitializer
@@ -52,7 +49,7 @@ class IPCSupportInitializer : public mojo::embedder::ProcessDelegate {
    private:
     // base::MessageLoop::DestructionObserver:
     void WillDestroyCurrentMessageLoop() override {
-      initializer_->ForceShutdown();
+      initializer_->ShutDown(true);
     }
 
     IPCSupportInitializer* initializer_;
@@ -112,24 +109,16 @@ void IPCSupportInitializer::Init(
   }
 }
 
-void IPCSupportInitializer::ShutDown() {
-  {
-    base::AutoLock locker(lock_);
-    if (shutting_down_ || was_shut_down_)
-      return;
-    DCHECK(init_count_ > 0);
-    if (init_count_ > 1) {
-      init_count_--;
-      return;
-    }
-  }
-  ForceShutdown();
-}
-
-void IPCSupportInitializer::ForceShutdown() {
+void IPCSupportInitializer::ShutDown(bool force) {
   base::AutoLock locker(lock_);
   if (shutting_down_ || was_shut_down_)
     return;
+  DCHECK(init_count_ > 0);
+  if (init_count_ > 1 && !force) {
+    init_count_--;
+    return;
+  }
+
   shutting_down_ = true;
   if (base::MessageLoop::current() &&
       base::MessageLoop::current()->task_runner() == io_thread_task_runner_) {
@@ -173,7 +162,7 @@ ScopedIPCSupport::ScopedIPCSupport(
 }
 
 ScopedIPCSupport::~ScopedIPCSupport() {
-  ipc_support_initializer.Get().ShutDown();
+  ipc_support_initializer.Get().ShutDown(false);
 }
 
 }  // namespace IPC