arc: Move singleton from ArcBridgeService to its Impl.

Move singleton design from ArcBridgeService to its impl. First step is to move
singleton from ArcBridgeService to its sub classes. Second step will be remove
singleton check from FakeArcBridgeService.

BUG=29942632
TEST=Not breaking any current tests.

Review-Url: https://codereview.chromium.org/2117623002
Cr-Commit-Position: refs/heads/master@{#403533}

components/arc/arc_bridge_service.cc

@@ -13,24 +13,16 @@
 
 namespace arc {
 
-namespace {
-
 // Weak pointer.  This class is owned by ArcServiceManager.
 ArcBridgeService* g_arc_bridge_service = nullptr;
 
-}  // namespace
-
 ArcBridgeService::ArcBridgeService()
     : available_(false), state_(State::STOPPED), weak_factory_(this) {
-  DCHECK(!g_arc_bridge_service);
-  g_arc_bridge_service = this;
 }
 
 ArcBridgeService::~ArcBridgeService() {
   DCHECK(CalledOnValidThread());
   DCHECK(state() == State::STOPPING || state() == State::STOPPED);
-  DCHECK(g_arc_bridge_service == this);
-  g_arc_bridge_service = nullptr;
 }
 
 // static

components/arc/arc_bridge_service_impl.cc

@@ -24,6 +24,8 @@
 
 namespace arc {
 
+extern ArcBridgeService* g_arc_bridge_service;
+
 namespace {
 constexpr int64_t kReconnectDelayInSeconds = 5;
 }  // namespace
@@ -34,10 +36,15 @@ ArcBridgeServiceImpl::ArcBridgeServiceImpl(
       binding_(this),
       session_started_(false),
       weak_factory_(this) {
+  DCHECK(!g_arc_bridge_service);
+  g_arc_bridge_service = this;
   bootstrap_->set_delegate(this);
 }
 
-ArcBridgeServiceImpl::~ArcBridgeServiceImpl() {}
+ArcBridgeServiceImpl::~ArcBridgeServiceImpl() {
+  DCHECK(g_arc_bridge_service == this);
+  g_arc_bridge_service = nullptr;
+}
 
 void ArcBridgeServiceImpl::HandleStartup() {
   DCHECK(CalledOnValidThread());

components/arc/test/fake_arc_bridge_service.cc

@@ -6,10 +6,16 @@
 
 namespace arc {
 
+extern ArcBridgeService* g_arc_bridge_service;
+
 FakeArcBridgeService::FakeArcBridgeService() {
+  DCHECK(!g_arc_bridge_service);
+  g_arc_bridge_service = this;
 }
 
 FakeArcBridgeService::~FakeArcBridgeService() {
+  DCHECK(g_arc_bridge_service == this);
+  g_arc_bridge_service = nullptr;
   SetStopped();
 }