[tracing] Fix MemoryDumpManager testing instance teardown pattern.

crrev.com/933613002 introduced a ODR violtaion by adding the
DeleteForTesting method (other definition in trace_event_impl.cc).
This was causing an ASan assertion (see crbug.com/459556) and failures
of base_unittests in debug builds (see crrev.com/933613002 #33).
This CL fixes the DeleteForTesting pattern removing the awkward ODR
violation.

BUG=459556,458295
TBR=nduca@chromium.org

Review URL: https://codereview.chromium.org/942803002

Cr-Commit-Position: refs/heads/master@{#317316}

base/trace_event/memory_dump_manager.cc

@@ -10,21 +10,13 @@
 #include "base/trace_event/memory_dump_provider.h"
 #include "base/trace_event/process_memory_dump.h"
 
-// TODO(primiano): in a separate CL rename DeleteTraceLogForTesting into
-// something like base::internal::TeardownSingletonForTesting so we don't have
-// to add a new friend to singleton each time.
-class DeleteTraceLogForTesting {
- public:
-  static void Delete() {
-    Singleton<
-        base::trace_event::MemoryDumpManager,
-        LeakySingletonTraits<base::trace_event::MemoryDumpManager>>::OnExit(0);
-  }
-};
-
 namespace base {
 namespace trace_event {
 
+namespace {
+MemoryDumpManager* g_instance_for_testing = nullptr;
+}
+
 // TODO(primiano): this should be smarter and should do something similar to
 // trace event synthetic delays.
 const char MemoryDumpManager::kTraceCategory[] =
@@ -32,13 +24,16 @@ const char MemoryDumpManager::kTraceCategory[] =
 
 // static
 MemoryDumpManager* MemoryDumpManager::GetInstance() {
+  if (g_instance_for_testing)
+    return g_instance_for_testing;
+
   return Singleton<MemoryDumpManager,
                    LeakySingletonTraits<MemoryDumpManager>>::get();
 }
 
 // static
-void MemoryDumpManager::DeleteForTesting() {
-  DeleteTraceLogForTesting::Delete();
+void MemoryDumpManager::SetInstanceForTesting(MemoryDumpManager* instance) {
+  g_instance_for_testing = instance;
 }
 
 MemoryDumpManager::MemoryDumpManager() : memory_tracing_enabled_(0) {

base/trace_event/memory_dump_manager.h

@@ -50,17 +50,17 @@ class BASE_EXPORT MemoryDumpManager : public TraceLog::EnabledStateObserver {
   void OnTraceLogDisabled() override;
 
  private:
+  friend struct DefaultDeleter<MemoryDumpManager>;  // For the testing instance.
   friend struct DefaultSingletonTraits<MemoryDumpManager>;
   friend class MemoryDumpManagerTest;
 
   static const char kTraceCategory[];
 
+  static void SetInstanceForTesting(MemoryDumpManager* instance);
+
   MemoryDumpManager();
   virtual ~MemoryDumpManager();
 
-  // Tears down the singleton instance.
-  static void DeleteForTesting();
-
   // Broadcasts the dump requests to the other processes.
   void BroadcastDumpRequest();
 

base/trace_event/memory_dump_manager_unittest.cc

@@ -17,14 +17,16 @@ namespace trace_event {
 class MemoryDumpManagerTest : public testing::Test {
  public:
   void SetUp() override {
+    mdm_.reset(new MemoryDumpManager());
+    MemoryDumpManager::SetInstanceForTesting(mdm_.get());
+    ASSERT_EQ(mdm_, MemoryDumpManager::GetInstance());
     MemoryDumpManager::GetInstance()->Initialize();
-    mdm_ = MemoryDumpManager::GetInstance();
   }
 
   void TearDown() override {
-    MemoryDumpManager::DeleteForTesting();
+    MemoryDumpManager::SetInstanceForTesting(nullptr);
+    mdm_.reset();
     TraceLog::DeleteForTesting();
-    mdm_ = NULL;
   }
 
  protected:
@@ -37,7 +39,7 @@ class MemoryDumpManagerTest : public testing::Test {
 
   void DisableTracing() { TraceLog::GetInstance()->SetDisabled(); }
 
-  MemoryDumpManager* mdm_;
+  scoped_ptr<MemoryDumpManager> mdm_;
 
  private:
   // We want our singleton torn down after each test.