Prevent DCHECK on shutdown of EmbeddedApplicationRunner

When EmbeddedApplicationRunner is destroyed, if the application
instance still has any bound connections, those connections must
be destroyed on the application task runner. Otherwise there is
a DCHECK failure when the binding is destroyed.

BUG=

Review-Url: https://codereview.chromium.org/2188503003
Cr-Commit-Position: refs/heads/master@{#408246}

content/common/mojo/embedded_application_runner.cc

@@ -52,13 +52,26 @@ class EmbeddedApplicationRunner::Instance
 
   void ShutDown() {
     DCHECK(runner_thread_checker_.CalledOnValidThread());
-    if (thread_) {
-      thread_.reset();
-      application_task_runner_ = nullptr;
+    if (!application_task_runner_)
+      return;
+    // Any extant ServiceContexts must be destroyed on the application thread.
+    if (application_task_runner_->BelongsToCurrentThread()) {
+      Quit();
+    } else {
+      application_task_runner_->PostTask(FROM_HERE,
+                                         base::Bind(&Instance::Quit, this));
     }
   }
 
  private:
+  friend class base::RefCountedThreadSafe<Instance>;
+
+  ~Instance() {
+    // If this instance had its own thread, it MUST be explicitly destroyed by
+    // QuitOnRunnerThread() by the time this destructor is run.
+    DCHECK(!thread_);
+  }
+
   void BindServiceRequestOnApplicationThread(
       shell::mojom::ServiceRequest request) {
     DCHECK(application_task_runner_->BelongsToCurrentThread());
@@ -76,15 +89,6 @@ class EmbeddedApplicationRunner::Instance
                    new_connection));
   }
 
- private:
-  friend class base::RefCountedThreadSafe<Instance>;
-
-  ~Instance() {
-    // If this instance had its own thread, it MUST be explicitly destroyed by
-    // ShutDown() on the runner's thread by the time this destructor is run.
-    DCHECK(!thread_);
-  }
-
   void OnStop(shell::ServiceContext* connection) {
     DCHECK(application_task_runner_->BelongsToCurrentThread());
 
@@ -102,13 +106,20 @@ class EmbeddedApplicationRunner::Instance
 
     shell_connections_.clear();
     service_.reset();
-    quit_task_runner_->PostTask(
-        FROM_HERE, base::Bind(&Instance::QuitOnRunnerThread, this));
+    if (quit_task_runner_->BelongsToCurrentThread()) {
+      QuitOnRunnerThread();
+    } else {
+      quit_task_runner_->PostTask(
+          FROM_HERE, base::Bind(&Instance::QuitOnRunnerThread, this));
+    }
   }
 
   void QuitOnRunnerThread() {
     DCHECK(runner_thread_checker_.CalledOnValidThread());
-    ShutDown();
+    if (thread_) {
+      thread_.reset();
+      application_task_runner_ = nullptr;
+    }
     quit_closure_.Run();
   }