tracing: Bail out early in tracing tests when tracing is already enabled

content/browser/tracing/memory_tracing_browsertest.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stdint.h>
 
 #include "base/bind.h"
 #include "base/callback_forward.h"
 #include "base/command_line.h"
 #include "base/run_loop.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/trace_event/memory_dump_manager.h"
 #include "base/trace_event/memory_dump_provider.h"
 #include "base/trace_event/memory_dump_request_args.h"
 #include "base/trace_event/trace_config_memory_test_util.h"
+#include "base/trace_event/trace_log.h"
 #include "content/public/browser/tracing_controller.h"
 #include "content/public/common/content_switches.h"
 #include "content/public/test/browser_test_utils.h"
 #include "content/public/test/content_browser_test.h"
 #include "content/public/test/content_browser_test_utils.h"
 #include "content/shell/browser/shell.h"
 #include "testing/gmock/include/gmock/gmock.h"
 
 using base::trace_event::MemoryDumpArgs;
 using base::trace_event::MemoryDumpLevelOfDetail;
@@ skipping 76 matching lines @@
   }
 
   void TearDown() override {
     MemoryDumpManager::GetInstance()->UnregisterDumpProvider(
         mock_dump_provider_.get());
     mock_dump_provider_.reset();
     ContentBrowserTest::TearDown();
   }
 
   void EnableMemoryTracing() {
+    CHECK(!base::trace_event::TraceLog::GetInstance()->IsEnabled())
+        << "Tracing seems to be already enabled. Very likely this is because "
+           "the startup tracing file has been leaked from a previous test.";
     // Enable tracing without periodic dumps.
     base::trace_event::TraceConfig trace_config(
         base::trace_event::TraceConfigMemoryTestUtil::
             GetTraceConfig_EmptyTriggers());
 
     base::RunLoop run_loop;
     bool success = TracingController::GetInstance()->StartTracing(
       trace_config, run_loop.QuitClosure());
     EXPECT_TRUE(success);
     run_loop.Run();
@@ skipping 187 matching lines @@
   EXPECT_CALL(*this, OnMemoryDumpDone(_, true /* success */));
 
   EnableMemoryTracing();
   RequestGlobalDumpAndWait(false /* from_renderer_thread */,
                            MemoryDumpType::EXPLICITLY_TRIGGERED,
                            MemoryDumpLevelOfDetail::DETAILED);
   DisableTracing();
 }
 
 }  // namespace content