[Chromoting] Introducing refcount-based life time management of the message loops in the service (d…

remoting/host/plugin/host_script_object.cc

Index: remoting/host/plugin/host_script_object.cc
diff --git a/remoting/host/plugin/host_script_object.cc b/remoting/host/plugin/host_script_object.cc
index 118114ff6f2a91f05cf2a7d0f1bdb6853149563c..8cffb5e4842b980c67dd3802c07dc576044459b3 100644
--- a/remoting/host/plugin/host_script_object.cc
+++ b/remoting/host/plugin/host_script_object.cc
@@ -15,6 +15,7 @@
 #include "base/utf_string_conversions.h"
 #include "base/values.h"
 #include "net/base/net_util.h"
+#include "remoting/base/auto_thread_task_runner.h"
 #include "remoting/base/auth_token_util.h"
 #include "remoting/host/chromoting_host.h"
 #include "remoting/host/chromoting_host_context.h"
@@ -106,6 +107,10 @@ HostNPScriptObject::~HostNPScriptObject() {
 
   HostLogHandler::UnregisterLoggingScriptObject(this);
 
+  // Stop the message loop. Any attempt to post a task to
+  // |context_.ui_task_runner()| will result in a CHECK() after this point.
+  // TODO(alexeypa): Enable posting messages to |plugin_task_runner_| during
+  // shutdown to avoid this hack.
   plugin_task_runner_->Detach();
 
   // Stop listening for policy updates.
@@ -121,9 +126,7 @@ HostNPScriptObject::~HostNPScriptObject() {
     // here because |host_context_| needs to be stopped on the plugin
     // thread, but the plugin thread may not exist after the instance
     // is destroyed.
-    disconnected_event_.Reset();
     DisconnectInternal();
-    disconnected_event_.Wait();
 
     // UI needs to be shut down on the UI thread before we destroy the
     // host context (because it depends on the context object), but
@@ -132,7 +135,15 @@ HostNPScriptObject::~HostNPScriptObject() {
     // unregister it from this thread).
     it2me_host_user_interface_.reset();
 
-    // Stops all threads.
+    // Release the context's TaskRunner references for the threads, so they can
+    // exit when no objects need them.
+    host_context_->ReleaseTaskRunners();
+
+    // |disconnected_event_| is signalled when the last reference to the plugin
+    // thread is dropped.
+    disconnected_event_.Wait();
+
+    // Stop all threads.
     host_context_.reset();
   }
 
@@ -143,7 +154,10 @@ bool HostNPScriptObject::Init() {
   DCHECK(plugin_task_runner_->BelongsToCurrentThread());
   VLOG(2) << "Init";
 
-  host_context_.reset(new ChromotingHostContext(plugin_task_runner_));
+  host_context_.reset(new ChromotingHostContext(new AutoThreadTaskRunner(
+      plugin_task_runner_,
+      base::Bind(&base::WaitableEvent::Signal,
+                 base::Unretained(&disconnected_event_)))));
   if (!host_context_->Start()) {
     host_context_.reset();
     return false;
@@ -878,13 +892,12 @@ void HostNPScriptObject::DisconnectInternal() {
 
   switch (state_) {
     case kDisconnected:
-      disconnected_event_.Signal();
       return;
 
     case kStarting:
+      desktop_environment_.reset();
       SetState(kDisconnecting);
       SetState(kDisconnected);
-      disconnected_event_.Signal();
       return;
 
     case kDisconnecting:
@@ -913,7 +926,7 @@ void HostNPScriptObject::DisconnectInternal() {
 void HostNPScriptObject::OnShutdownFinished() {
   DCHECK(host_context_->network_task_runner()->BelongsToCurrentThread());
 
-  disconnected_event_.Signal();
+  desktop_environment_.reset();
 }
 
 void HostNPScriptObject::OnPolicyUpdate(