Add assertions to ensure that only one instance of RemoteTestServer is

net/test/spawned_test_server/remote_test_server.cc

Index: net/test/spawned_test_server/remote_test_server.cc
diff --git a/net/test/spawned_test_server/remote_test_server.cc b/net/test/spawned_test_server/remote_test_server.cc
index c563242bb3c66e9991178279c073eb5eb43e81da..1baab8ceab6bfa672c9f7648736edb74ac7de21a 100644
--- a/net/test/spawned_test_server/remote_test_server.cc
+++ b/net/test/spawned_test_server/remote_test_server.cc
@@ -13,6 +13,7 @@
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/json/json_writer.h"
+#include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/path_service.h"
 #include "base/strings/string_number_conversions.h"
@@ -27,6 +28,31 @@ namespace net {
 
 namespace {
 
+// Based on how the Android runner sets things up, it is only valid for one
+// RemoteTestServer to be active on the device at a time.
+class RemoteTestServerTracker {
+ public:
+  void StartingServer() {
+    base::AutoLock l(lock_);
+    CHECK_EQ(count_, 0);
+    count_++;
+  }
+
+  void StoppingServer() {
+    base::AutoLock l(lock_);
+    CHECK_EQ(count_, 1);
+    count_--;
+  }
+
+ private:
+  // |lock_| protects access to |count_|.
+  base::Lock lock_;
+  int count_ = 0;
+};
+
+base::LazyInstance<RemoteTestServerTracker>::Leaky tracker =
+    LAZY_INSTANCE_INITIALIZER;
+
 // To reduce the running time of tests, tests may be sharded across several
 // devices. This means that it may be necessary to support multiple instances
 // of the test server spawner and the Python test server simultaneously on the
@@ -92,6 +118,9 @@ RemoteTestServer::~RemoteTestServer() {
 bool RemoteTestServer::Start() {
   if (spawner_communicator_.get())
     return true;
+
+  tracker.Get().StartingServer();
+
   spawner_communicator_.reset(new SpawnerCommunicator(spawner_server_port_));
 
   base::DictionaryValue arguments_dict;
@@ -148,8 +177,15 @@ bool RemoteTestServer::BlockUntilStarted() {
 bool RemoteTestServer::Stop() {
   if (!spawner_communicator_.get())
     return true;
+
+  tracker.Get().StoppingServer();
+
   CleanUpWhenStoppingServer();
   bool stopped = spawner_communicator_->StopServer();
+
+  if (!stopped)
+    LOG(ERROR) << "Failed stopping RemoteTestServer";
+
   // Explicitly reset |spawner_communicator_| to avoid reusing the stopped one.
   spawner_communicator_.reset(NULL);
   return stopped;