Add TRACE_EVENT_IS_NEW_TRACE as a way to snapshot objects at start of recording

base/debug/trace_event_unittest.cc

 // Copyright (c) 2012 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 "base/debug/trace_event_unittest.h"
 
 #include <cstdlib>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 887 matching lines @@
 
   EXPECT_CALL(observer, OnTraceLogWillDisable())
       .Times(1);
   TraceLog::GetInstance()->SetDisabled();
   testing::Mock::VerifyAndClear(&observer);
 
   // Cleanup.
   TraceLog::GetInstance()->RemoveEnabledStateObserver(&observer);
 }
 
+bool IsNewTrace() {
+  bool is_new_trace;
+  TRACE_EVENT_IS_NEW_TRACE(&is_new_trace);
+  return is_new_trace;
+}
+
+TEST_F(TraceEventTestFixture, NewTraceRecording) {
+  ManualTestSetUp();
+  ASSERT_FALSE(IsNewTrace());
+  TraceLog::GetInstance()->SetEnabled(CategoryFilter("*"),
+                                      TraceLog::RECORD_UNTIL_FULL);
+  // First call to IsNewTrace() should succeed. But, the second shouldn't.
+  ASSERT_TRUE(IsNewTrace());
+  ASSERT_FALSE(IsNewTrace());
+  EndTraceAndFlush();
+
+  // IsNewTrace() should definitely be false now.
+  ASSERT_FALSE(IsNewTrace());
+
+  // Start another trace. IsNewTrace() should become true again, briefly, as
+  // before.
+  TraceLog::GetInstance()->SetEnabled(CategoryFilter("*"),
+                                      TraceLog::RECORD_UNTIL_FULL);
+  ASSERT_TRUE(IsNewTrace());
+  ASSERT_FALSE(IsNewTrace());
+
+  // Cleanup.
+  EndTraceAndFlush();
+}
+
+
 // Test that categories work.
 TEST_F(TraceEventTestFixture, Categories) {
   ManualTestSetUp();
 
   // Test that categories that are used can be retrieved whether trace was
   // enabled or disabled when the trace event was encountered.
   TRACE_EVENT_INSTANT0("c1", "name", TRACE_EVENT_SCOPE_THREAD);
   TRACE_EVENT_INSTANT0("c2", "name", TRACE_EVENT_SCOPE_THREAD);
   BeginTrace();
   TRACE_EVENT_INSTANT0("c3", "name", TRACE_EVENT_SCOPE_THREAD);
@@ skipping 1078 matching lines @@
   EXPECT_TRUE(CategoryFilter::IsEmptyOrContainsLeadingOrTrailingWhitespace(
       "   bad_category   "));
   EXPECT_TRUE(CategoryFilter::IsEmptyOrContainsLeadingOrTrailingWhitespace(
       ""));
   EXPECT_FALSE(CategoryFilter::IsEmptyOrContainsLeadingOrTrailingWhitespace(
       "good_category"));
 }
 
 }  // namespace debug
 }  // namespace base