Move tracing namespace from base::debug to base::trace_event.

After having transitioned all the tracing headers from base/debug/ to
base/trace_event, this CL addresses the namespace move.
In principle, this CL should only change the namespace of the
base/trace_event files but the namespace used by the tracing clients.
In order to achieve this, namespace aliases are appended to the
trace_event headers, to make it so that clients can still refer to
base::debug::TraceFoo, with that being aliased to
base::trace_event::TraceFoo.
The upcoming CLs will gradually migrate the clients to use the
base::trace_event namespace and will remove the ns aliases.
Unfortunately, this CL has also to update few tracing clients,
in particular the ones having forward declarations. Forward
declarations, in fact, cannot be aliased as the compiler sees them
before the alias itself.

See crrev.com/837303004 and the related bug for motivations and design doc.

BUG=451032
TBR=skyostil@chromium.org,jam@chromium.org

Review URL: https://codereview.chromium.org/882673002

Cr-Commit-Position: refs/heads/master@{#314657}

21 files changed, 161 insertions, 105 deletions

diff --git a/base/trace_event/trace_event.h b/base/trace_event/trace_event.h
index 7f73071..a4c4f83 100644
--- a/base/trace_event/trace_event.h
+++ b/base/trace_event/trace_event.h
@@ -141,7 +141,7 @@
 // means, if the category for the event is disabled, the conversion will not
 // happen.
 //
-//   class MyData : public base::debug::ConvertableToTraceFormat {
+//   class MyData : public base::trace_event::ConvertableToTraceFormat {
 //    public:
 //     MyData() {}
 //     virtual void AppendAsTraceFormat(std::string* out) const override {
@@ -795,8 +795,8 @@
 
 #define INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE() \
     UNLIKELY(*INTERNAL_TRACE_EVENT_UID(category_group_enabled) & \
-        (base::debug::TraceLog::ENABLED_FOR_RECORDING | \
-         base::debug::TraceLog::ENABLED_FOR_EVENT_CALLBACK))
+        (base::trace_event::TraceLog::ENABLED_FOR_RECORDING | \
+         base::trace_event::TraceLog::ENABLED_FOR_EVENT_CALLBACK))
 
 // Macro to efficiently determine if a given category group is enabled.
 #define TRACE_EVENT_CATEGORY_GROUP_ENABLED(category_group, ret) \
@@ -839,16 +839,16 @@
 // const unsigned char*
 //     TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED(const char* category_group)
 #define TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED \
-    base::debug::TraceLog::GetCategoryGroupEnabled
+    base::trace_event::TraceLog::GetCategoryGroupEnabled
 
 // Get the number of times traces have been recorded. This is used to implement
 // the TRACE_EVENT_IS_NEW_TRACE facility.
 // unsigned int TRACE_EVENT_API_GET_NUM_TRACES_RECORDED()
 #define TRACE_EVENT_API_GET_NUM_TRACES_RECORDED \
-    base::debug::TraceLog::GetInstance()->GetNumTracesRecorded
+    base::trace_event::TraceLog::GetInstance()->GetNumTracesRecorded
 
 // Add a trace event to the platform tracing system.
-// base::debug::TraceEventHandle TRACE_EVENT_API_ADD_TRACE_EVENT(
+// base::trace_event::TraceEventHandle TRACE_EVENT_API_ADD_TRACE_EVENT(
 //                    char phase,
 //                    const unsigned char* category_group_enabled,
 //                    const char* name,
@@ -859,10 +859,11 @@
 //                    const unsigned long long* arg_values,
 //                    unsigned char flags)
 #define TRACE_EVENT_API_ADD_TRACE_EVENT \
-    base::debug::TraceLog::GetInstance()->AddTraceEvent
+    base::trace_event::TraceLog::GetInstance()->AddTraceEvent
 
 // Add a trace event to the platform tracing system.
-// base::debug::TraceEventHandle TRACE_EVENT_API_ADD_TRACE_EVENT_WITH_TIMESTAMP(
+// base::trace_event::TraceEventHandle
+// TRACE_EVENT_API_ADD_TRACE_EVENT_WITH_TIMESTAMP(
 //                    char phase,
 //                    const unsigned char* category_group_enabled,
 //                    const char* name,
@@ -875,15 +876,16 @@
 //                    const unsigned long long* arg_values,
 //                    unsigned char flags)
 #define TRACE_EVENT_API_ADD_TRACE_EVENT_WITH_THREAD_ID_AND_TIMESTAMP \
-    base::debug::TraceLog::GetInstance()->AddTraceEventWithThreadIdAndTimestamp
+    base::trace_event::TraceLog::GetInstance() \
+      ->AddTraceEventWithThreadIdAndTimestamp
 
 // Set the duration field of a COMPLETE trace event.
 // void TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(
 //     const unsigned char* category_group_enabled,
 //     const char* name,
-//     base::debug::TraceEventHandle id)
+//     base::trace_event::TraceEventHandle id)
 #define TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION \
-    base::debug::TraceLog::GetInstance()->UpdateTraceEventDuration
+    base::trace_event::TraceLog::GetInstance()->UpdateTraceEventDuration
 
 // Defines atomic operations used internally by the tracing system.
 #define TRACE_EVENT_API_ATOMIC_WORD base::subtle::AtomicWord
@@ -956,11 +958,12 @@ TRACE_EVENT_API_CLASS_EXPORT extern \
     INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group); \
     trace_event_internal::ScopedTracer INTERNAL_TRACE_EVENT_UID(tracer); \
     if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) { \
-      base::debug::TraceEventHandle h = trace_event_internal::AddTraceEvent( \
-          TRACE_EVENT_PHASE_COMPLETE, \
-          INTERNAL_TRACE_EVENT_UID(category_group_enabled), \
-          name, trace_event_internal::kNoEventId, \
-          TRACE_EVENT_FLAG_NONE, ##__VA_ARGS__); \
+      base::trace_event::TraceEventHandle h = \
+          trace_event_internal::AddTraceEvent( \
+              TRACE_EVENT_PHASE_COMPLETE, \
+              INTERNAL_TRACE_EVENT_UID(category_group_enabled), name, \
+              trace_event_internal::kNoEventId, TRACE_EVENT_FLAG_NONE, \
+              ##__VA_ARGS__); \
       INTERNAL_TRACE_EVENT_UID(tracer).Initialize( \
           INTERNAL_TRACE_EVENT_UID(category_group_enabled), name, h); \
     }
@@ -1253,7 +1256,7 @@ static inline void SetTraceValue(const base::TimeTicks arg,
 // pointers to the internal c_str and pass through to the tracing API,
 // the arg_values must live throughout these procedures.
 
-static inline base::debug::TraceEventHandle
+static inline base::trace_event::TraceEventHandle
 AddTraceEventWithThreadIdAndTimestamp(
     char phase,
     const unsigned char* category_group_enabled,
@@ -1263,7 +1266,8 @@ AddTraceEventWithThreadIdAndTimestamp(
     const base::TimeTicks& timestamp,
     unsigned char flags,
     const char* arg1_name,
-    const scoped_refptr<base::debug::ConvertableToTraceFormat>& arg1_val) {
+    const scoped_refptr<base::trace_event::ConvertableToTraceFormat>&
+        arg1_val) {
   const int num_args = 1;
   unsigned char arg_types[1] = { TRACE_VALUE_TYPE_CONVERTABLE };
   return TRACE_EVENT_API_ADD_TRACE_EVENT_WITH_THREAD_ID_AND_TIMESTAMP(
@@ -1272,7 +1276,7 @@ AddTraceEventWithThreadIdAndTimestamp(
 }
 
 template<class ARG1_TYPE>
-static inline base::debug::TraceEventHandle
+static inline base::trace_event::TraceEventHandle
 AddTraceEventWithThreadIdAndTimestamp(
     char phase,
     const unsigned char* category_group_enabled,
@@ -1284,7 +1288,8 @@ AddTraceEventWithThreadIdAndTimestamp(
     const char* arg1_name,
     const ARG1_TYPE& arg1_val,
     const char* arg2_name,
-    const scoped_refptr<base::debug::ConvertableToTraceFormat>& arg2_val) {
+    const scoped_refptr<base::trace_event::ConvertableToTraceFormat>&
+        arg2_val) {
   const int num_args = 2;
   const char* arg_names[2] = { arg1_name, arg2_name };
 
@@ -1293,7 +1298,8 @@ AddTraceEventWithThreadIdAndTimestamp(
   SetTraceValue(arg1_val, &arg_types[0], &arg_values[0]);
   arg_types[1] = TRACE_VALUE_TYPE_CONVERTABLE;
 
-  scoped_refptr<base::debug::ConvertableToTraceFormat> convertable_values[2];
+  scoped_refptr<base::trace_event::ConvertableToTraceFormat>
+      convertable_values[2];
   convertable_values[1] = arg2_val;
 
   return TRACE_EVENT_API_ADD_TRACE_EVENT_WITH_THREAD_ID_AND_TIMESTAMP(
@@ -1302,7 +1308,7 @@ AddTraceEventWithThreadIdAndTimestamp(
 }
 
 template<class ARG2_TYPE>
-static inline base::debug::TraceEventHandle
+static inline base::trace_event::TraceEventHandle
 AddTraceEventWithThreadIdAndTimestamp(
     char phase,
     const unsigned char* category_group_enabled,
@@ -1312,7 +1318,7 @@ AddTraceEventWithThreadIdAndTimestamp(
     const base::TimeTicks& timestamp,
     unsigned char flags,
     const char* arg1_name,
-    const scoped_refptr<base::debug::ConvertableToTraceFormat>& arg1_val,
+    const scoped_refptr<base::trace_event::ConvertableToTraceFormat>& arg1_val,
     const char* arg2_name,
     const ARG2_TYPE& arg2_val) {
   const int num_args = 2;
@@ -1324,7 +1330,8 @@ AddTraceEventWithThreadIdAndTimestamp(
   arg_values[0] = 0;
   SetTraceValue(arg2_val, &arg_types[1], &arg_values[1]);
 
-  scoped_refptr<base::debug::ConvertableToTraceFormat> convertable_values[2];
+  scoped_refptr<base::trace_event::ConvertableToTraceFormat>
+      convertable_values[2];
   convertable_values[0] = arg1_val;
 
   return TRACE_EVENT_API_ADD_TRACE_EVENT_WITH_THREAD_ID_AND_TIMESTAMP(
@@ -1332,7 +1339,7 @@ AddTraceEventWithThreadIdAndTimestamp(
       num_args, arg_names, arg_types, arg_values, convertable_values, flags);
 }
 
-static inline base::debug::TraceEventHandle
+static inline base::trace_event::TraceEventHandle
 AddTraceEventWithThreadIdAndTimestamp(
     char phase,
     const unsigned char* category_group_enabled,
@@ -1342,22 +1349,23 @@ AddTraceEventWithThreadIdAndTimestamp(
     const base::TimeTicks& timestamp,
     unsigned char flags,
     const char* arg1_name,
-    const scoped_refptr<base::debug::ConvertableToTraceFormat>& arg1_val,
+    const scoped_refptr<base::trace_event::ConvertableToTraceFormat>& arg1_val,
     const char* arg2_name,
-    const scoped_refptr<base::debug::ConvertableToTraceFormat>& arg2_val) {
+    const scoped_refptr<base::trace_event::ConvertableToTraceFormat>&
+        arg2_val) {
   const int num_args = 2;
   const char* arg_names[2] = { arg1_name, arg2_name };
   unsigned char arg_types[2] =
       { TRACE_VALUE_TYPE_CONVERTABLE, TRACE_VALUE_TYPE_CONVERTABLE };
-  scoped_refptr<base::debug::ConvertableToTraceFormat> convertable_values[2] =
-      { arg1_val, arg2_val };
+  scoped_refptr<base::trace_event::ConvertableToTraceFormat>
+      convertable_values[2] = {arg1_val, arg2_val};
 
   return TRACE_EVENT_API_ADD_TRACE_EVENT_WITH_THREAD_ID_AND_TIMESTAMP(
       phase, category_group_enabled, name, id, thread_id, timestamp,
       num_args, arg_names, arg_types, NULL, convertable_values, flags);
 }
 
-static inline base::debug::TraceEventHandle
+static inline base::trace_event::TraceEventHandle
 AddTraceEventWithThreadIdAndTimestamp(
     char phase,
     const unsigned char* category_group_enabled,
@@ -1371,7 +1379,7 @@ AddTraceEventWithThreadIdAndTimestamp(
       kZeroNumArgs, NULL, NULL, NULL, NULL, flags);
 }
 
-static inline base::debug::TraceEventHandle AddTraceEvent(
+static inline base::trace_event::TraceEventHandle AddTraceEvent(
     char phase,
     const unsigned char* category_group_enabled,
     const char* name,
@@ -1384,7 +1392,7 @@ static inline base::debug::TraceEventHandle AddTraceEvent(
 }
 
 template<class ARG1_TYPE>
-static inline base::debug::TraceEventHandle
+static inline base::trace_event::TraceEventHandle
 AddTraceEventWithThreadIdAndTimestamp(
     char phase,
     const unsigned char* category_group_enabled,
@@ -1405,7 +1413,7 @@ AddTraceEventWithThreadIdAndTimestamp(
 }
 
 template<class ARG1_TYPE>
-static inline base::debug::TraceEventHandle AddTraceEvent(
+static inline base::trace_event::TraceEventHandle AddTraceEvent(
     char phase,
     const unsigned char* category_group_enabled,
     const char* name,
@@ -1421,7 +1429,7 @@ static inline base::debug::TraceEventHandle AddTraceEvent(
 }
 
 template<class ARG1_TYPE, class ARG2_TYPE>
-static inline base::debug::TraceEventHandle
+static inline base::trace_event::TraceEventHandle
 AddTraceEventWithThreadIdAndTimestamp(
     char phase,
     const unsigned char* category_group_enabled,
@@ -1446,7 +1454,7 @@ AddTraceEventWithThreadIdAndTimestamp(
 }
 
 template<class ARG1_TYPE, class ARG2_TYPE>
-static inline base::debug::TraceEventHandle AddTraceEvent(
+static inline base::trace_event::TraceEventHandle AddTraceEvent(
     char phase,
     const unsigned char* category_group_enabled,
     const char* name,
@@ -1478,7 +1486,7 @@ class TRACE_EVENT_API_CLASS_EXPORT ScopedTracer {
 
   void Initialize(const unsigned char* category_group_enabled,
                   const char* name,
-                  base::debug::TraceEventHandle event_handle) {
+                  base::trace_event::TraceEventHandle event_handle) {
     data_.category_group_enabled = category_group_enabled;
     data_.name = name;
     data_.event_handle = event_handle;
@@ -1494,7 +1502,7 @@ class TRACE_EVENT_API_CLASS_EXPORT ScopedTracer {
   struct Data {
     const unsigned char* category_group_enabled;
     const char* name;
-    base::debug::TraceEventHandle event_handle;
+    base::trace_event::TraceEventHandle event_handle;
   };
   Data* p_data_;
   Data data_;
@@ -1509,7 +1517,7 @@ class TRACE_EVENT_API_CLASS_EXPORT ScopedTraceBinaryEfficient {
  private:
   const unsigned char* category_group_enabled_;
   const char* name_;
-  base::debug::TraceEventHandle event_handle_;
+  base::trace_event::TraceEventHandle event_handle_;
 };
 
 // This macro generates less code then TRACE_EVENT0 but is also
@@ -1555,7 +1563,7 @@ class TraceEventSamplingStateScope {
 }  // namespace trace_event_internal
 
 namespace base {
-namespace debug {
+namespace trace_event {
 
 template<typename IDType> class TraceScopedTrackableObject {
  public:
@@ -1583,7 +1591,15 @@ template<typename IDType> class TraceScopedTrackableObject {
   DISALLOW_COPY_AND_ASSIGN(TraceScopedTrackableObject);
 };
 
-} // namespace debug
-} // namespace base
+}  // namespace trace_event
+}  // namespace base
+
+// TODO(ssid): remove these aliases after the tracing clients are moved to the
+// new trace_event namespace. See crbug.com/451032. ETA: March 2015.
+namespace base {
+namespace debug {
+using base::trace_event::TraceScopedTrackableObject;
+}  // namespace debug
+}  // namespace base
 
 #endif /* BASE_TRACE_EVENT_TRACE_EVENT_H_ */
diff --git a/base/trace_event/trace_event_android.cc b/base/trace_event/trace_event_android.cc
index 31da26d..bcba436 100644
--- a/base/trace_event/trace_event_android.cc
+++ b/base/trace_event/trace_event_android.cc
@@ -24,8 +24,8 @@ void WriteEvent(
     unsigned long long id,
     const char** arg_names,
     const unsigned char* arg_types,
-    const base::debug::TraceEvent::TraceValue* arg_values,
-    const scoped_refptr<base::debug::ConvertableToTraceFormat>*
+    const base::trace_event::TraceEvent::TraceValue* arg_values,
+    const scoped_refptr<base::trace_event::ConvertableToTraceFormat>*
         convertable_values,
     unsigned char flags) {
   std::string out = base::StringPrintf("%c|%d|%s", phase, getpid(), name);
@@ -33,7 +33,8 @@ void WriteEvent(
     base::StringAppendF(&out, "-%" PRIx64, static_cast<uint64>(id));
   out += '|';
 
-  for (int i = 0; i < base::debug::kTraceMaxNumArgs && arg_names[i]; ++i) {
+  for (int i = 0; i < base::trace_event::kTraceMaxNumArgs && arg_names[i];
+       ++i) {
     if (i)
       out += ';';
     out += arg_names[i];
@@ -42,8 +43,8 @@ void WriteEvent(
     if (arg_types[i] == TRACE_VALUE_TYPE_CONVERTABLE) {
       convertable_values[i]->AppendAsTraceFormat(&out);
     } else {
-      base::debug::TraceEvent::AppendValueAsJSON(
-          arg_types[i], arg_values[i], &out);
+      base::trace_event::TraceEvent::AppendValueAsJSON(arg_types[i],
+                                                       arg_values[i], &out);
     }
     // Remove the quotes which may confuse the atrace script.
     ReplaceSubstringsAfterOffset(&out, value_start, "\\\"", "'");
@@ -65,7 +66,7 @@ void NoOpOutputCallback(base::WaitableEvent* complete_event,
     complete_event->Signal();
 }
 
-void EndChromeTracing(base::debug::TraceLog* trace_log,
+void EndChromeTracing(base::trace_event::TraceLog* trace_log,
                       base::WaitableEvent* complete_event) {
   trace_log->SetDisabled();
   // Delete the buffered trace events as they have been sent to atrace.
@@ -75,7 +76,7 @@ void EndChromeTracing(base::debug::TraceLog* trace_log,
 }  // namespace
 
 namespace base {
-namespace debug {
+namespace trace_event {
 
 // These functions support Android systrace.py when 'webview' category is
 // traced. With the new adb_profile_chrome, we may have two phases:
@@ -195,5 +196,5 @@ void TraceLog::AddClockSyncMetadataEvent() {
   close(atrace_fd);
 }
 
-}  // namespace debug
+}  // namespace trace_event
 }  // namespace base
diff --git a/base/trace_event/trace_event_argument.cc b/base/trace_event/trace_event_argument.cc
index 00fcde1..91ed9e8 100644
--- a/base/trace_event/trace_event_argument.cc
+++ b/base/trace_event/trace_event_argument.cc
@@ -8,7 +8,7 @@
 #include "base/values.h"
 
 namespace base {
-namespace debug {
+namespace trace_event {
 
 TracedValue::TracedValue() : root_(new DictionaryValue()) {
   stack_.push_back(root_.get());
@@ -113,5 +113,5 @@ void TracedValue::AppendAsTraceFormat(std::string* out) const {
   DCHECK_EQ(1u, stack_.size()) << tmp;
 }
 
-}  // namespace debug
+}  // namespace trace_event
 }  // namespace base
diff --git a/base/trace_event/trace_event_argument.h b/base/trace_event/trace_event_argument.h
index 08a5b50..43a0f38 100644
--- a/base/trace_event/trace_event_argument.h
+++ b/base/trace_event/trace_event_argument.h
@@ -16,7 +16,7 @@ class DictionaryValue;
 class ListValue;
 class Value;
 
-namespace debug {
+namespace trace_event {
 
 class BASE_EXPORT TracedValue : public ConvertableToTraceFormat {
  public:
@@ -53,6 +53,14 @@ class BASE_EXPORT TracedValue : public ConvertableToTraceFormat {
   DISALLOW_COPY_AND_ASSIGN(TracedValue);
 };
 
+}  // namespace trace_event
+}  // namespace base
+
+// TODO(ssid): remove these aliases after the tracing clients are moved to the
+// new trace_event namespace. See crbug.com/451032. ETA: March 2015.
+namespace base {
+namespace debug {
+using base::trace_event::TracedValue;
 }  // namespace debug
 }  // namespace base
 
diff --git a/base/trace_event/trace_event_argument_unittest.cc b/base/trace_event/trace_event_argument_unittest.cc
index 39cafef..c59910e 100644
--- a/base/trace_event/trace_event_argument_unittest.cc
+++ b/base/trace_event/trace_event_argument_unittest.cc
@@ -6,7 +6,7 @@
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
-namespace debug {
+namespace trace_event {
 
 TEST(TraceEventArgumentTest, FlatDictionary) {
   scoped_refptr<TracedValue> value = new TracedValue();
@@ -49,5 +49,5 @@ TEST(TraceEventArgumentTest, Hierarchy) {
       json);
 }
 
-}  // namespace debug
+}  // namespace trace_event
 }  // namespace base
diff --git a/base/trace_event/trace_event_impl.cc b/base/trace_event/trace_event_impl.cc
index a8a0cc1..95cf06d 100644
--- a/base/trace_event/trace_event_impl.cc
+++ b/base/trace_event/trace_event_impl.cc
@@ -41,8 +41,8 @@
 class DeleteTraceLogForTesting {
  public:
   static void Delete() {
-    Singleton<base::debug::TraceLog,
-              LeakySingletonTraits<base::debug::TraceLog> >::OnExit(0);
+    Singleton<base::trace_event::TraceLog,
+              LeakySingletonTraits<base::trace_event::TraceLog>>::OnExit(0);
   }
 };
 
@@ -50,7 +50,7 @@ class DeleteTraceLogForTesting {
 BASE_EXPORT TRACE_EVENT_API_ATOMIC_WORD g_trace_state[3];
 
 namespace base {
-namespace debug {
+namespace trace_event {
 
 namespace {
 
@@ -2560,7 +2560,7 @@ const CategoryFilter::StringList&
   return delays_;
 }
 
-}  // namespace debug
+}  // namespace trace_event
 }  // namespace base
 
 namespace trace_event_internal {
diff --git a/base/trace_event/trace_event_impl.h b/base/trace_event/trace_event_impl.h
index 6d04c76..742f6b6 100644
--- a/base/trace_event/trace_event_impl.h
+++ b/base/trace_event/trace_event_impl.h
@@ -27,17 +27,17 @@
 // Older style trace macros with explicit id and extra data
 // Only these macros result in publishing data to ETW as currently implemented.
 #define TRACE_EVENT_BEGIN_ETW(name, id, extra) \
-    base::debug::TraceLog::AddTraceEventEtw( \
+    base::trace_event::TraceLog::AddTraceEventEtw( \
         TRACE_EVENT_PHASE_BEGIN, \
         name, reinterpret_cast<const void*>(id), extra)
 
 #define TRACE_EVENT_END_ETW(name, id, extra) \
-    base::debug::TraceLog::AddTraceEventEtw( \
+    base::trace_event::TraceLog::AddTraceEventEtw( \
         TRACE_EVENT_PHASE_END, \
         name, reinterpret_cast<const void*>(id), extra)
 
 #define TRACE_EVENT_INSTANT_ETW(name, id, extra) \
-    base::debug::TraceLog::AddTraceEventEtw( \
+    base::trace_event::TraceLog::AddTraceEventEtw( \
         TRACE_EVENT_PHASE_INSTANT, \
         name, reinterpret_cast<const void*>(id), extra)
 
@@ -49,7 +49,7 @@ namespace base {
 class WaitableEvent;
 class MessageLoop;
 
-namespace debug {
+namespace trace_event {
 
 // For any argument of type TRACE_VALUE_TYPE_CONVERTABLE the provided
 // class must implement this interface.
@@ -807,6 +807,23 @@ class BASE_EXPORT TraceLog {
   DISALLOW_COPY_AND_ASSIGN(TraceLog);
 };
 
+}  // namespace trace_event
+}  // namespace base
+
+// TODO(ssid): remove these aliases after the tracing clients are moved to the
+// new trace_event namespace. See crbug.com/451032. ETA: March 2015.
+namespace base {
+namespace debug {
+using base::trace_event::CategoryFilter;
+using base::trace_event::ConvertableToTraceFormat;
+using base::trace_event::RECORD_UNTIL_FULL;
+using base::trace_event::RECORD_CONTINUOUSLY;
+using base::trace_event::RECORD_AS_MUCH_AS_POSSIBLE;
+using base::trace_event::TraceEventHandle;
+using base::trace_event::TraceLog;
+using base::trace_event::TraceLogStatus;
+using base::trace_event::TraceOptions;
+using base::trace_event::TraceResultBuffer;
 }  // namespace debug
 }  // namespace base
 
diff --git a/base/trace_event/trace_event_impl_constants.cc b/base/trace_event/trace_event_impl_constants.cc
index c46cf49..ffeacff 100644
--- a/base/trace_event/trace_event_impl_constants.cc
+++ b/base/trace_event/trace_event_impl_constants.cc
@@ -5,7 +5,7 @@
 #include "base/trace_event/trace_event_impl.h"
 
 namespace base {
-namespace debug {
+namespace trace_event {
 
 // Enable everything but debug and test categories by default.
 const char CategoryFilter::kDefaultCategoryFilterString[] = "-*Debug,-*Test";
@@ -24,5 +24,5 @@ const TraceLog::InternalTraceOptions
 const TraceLog::InternalTraceOptions
     TraceLog::kInternalRecordAsMuchAsPossible = 1 << 4;
 
-}  // namespace debug
+}  // namespace trace_event
 }  // namespace base
diff --git a/base/trace_event/trace_event_memory.cc b/base/trace_event/trace_event_memory.cc
index 96b28e4..2bf6d38 100644
--- a/base/trace_event/trace_event_memory.cc
+++ b/base/trace_event/trace_event_memory.cc
@@ -15,7 +15,7 @@
 #include "base/trace_event/trace_event.h"
 
 namespace base {
-namespace debug {
+namespace trace_event {
 
 namespace {
 
@@ -26,13 +26,13 @@ const size_t kMaxScopeDepth = 16;
 
 /////////////////////////////////////////////////////////////////////////////
 // Holds a memory dump until the tracing system needs to serialize it.
-class MemoryDumpHolder : public base::debug::ConvertableToTraceFormat {
+class MemoryDumpHolder : public base::trace_event::ConvertableToTraceFormat {
  public:
   // Takes ownership of dump, which must be a JSON string, allocated with
   // malloc() and NULL terminated.
   explicit MemoryDumpHolder(char* dump) : dump_(dump) {}
 
-  // base::debug::ConvertableToTraceFormat overrides:
+  // base::trace_event::ConvertableToTraceFormat overrides:
   void AppendAsTraceFormat(std::string* out) const override {
     AppendHeapProfileAsTraceFormat(dump_, out);
   }
@@ -165,7 +165,7 @@ TraceMemoryController::~TraceMemoryController() {
   TraceLog::GetInstance()->RemoveEnabledStateObserver(this);
 }
 
-  // base::debug::TraceLog::EnabledStateChangedObserver overrides:
+// base::trace_event::TraceLog::EnabledStateChangedObserver overrides:
 void TraceMemoryController::OnTraceLogEnabled() {
   // Check to see if tracing is enabled for the memory category.
   bool enabled;
@@ -436,5 +436,5 @@ const char* StringFromHexAddress(const std::string& hex_address) {
   return reinterpret_cast<const char*>(address);
 }
 
-}  // namespace debug
+}  // namespace trace_event
 }  // namespace base
diff --git a/base/trace_event/trace_event_memory.h b/base/trace_event/trace_event_memory.h
index f16467f..8e70020 100644
--- a/base/trace_event/trace_event_memory.h
+++ b/base/trace_event/trace_event_memory.h
@@ -22,7 +22,7 @@ namespace base {
 
 class MessageLoopProxy;
 
-namespace debug {
+namespace trace_event {
 
 // Watches for chrome://tracing to be enabled or disabled. When tracing is
 // enabled, also enables tcmalloc heap profiling. This class is the preferred
@@ -46,7 +46,7 @@ class BASE_EXPORT TraceMemoryController
       GetHeapProfileFunction get_heap_profile_function);
   virtual ~TraceMemoryController();
 
-  // base::debug::TraceLog::EnabledStateChangedObserver overrides:
+  // base::trace_event::TraceLog::EnabledStateChangedObserver overrides:
   void OnTraceLogEnabled() override;
   void OnTraceLogDisabled() override;
 
@@ -146,7 +146,7 @@ BASE_EXPORT bool AppendHeapProfileLineAsTraceFormat(const std::string& line,
 // and "error" if |address| could not be parsed. Visible for testing.
 BASE_EXPORT const char* StringFromHexAddress(const std::string& hex_address);
 
-}  // namespace debug
+}  // namespace trace_event
 }  // namespace base
 
 // Make local variables with unique names based on the line number. Note that
@@ -159,7 +159,7 @@ BASE_EXPORT const char* StringFromHexAddress(const std::string& hex_address);
 // It generates a unique local variable name using the macros above.
 #if defined(TCMALLOC_TRACE_MEMORY_SUPPORTED)
 #define INTERNAL_TRACE_MEMORY(category, name) \
-  base::debug::ScopedTraceMemory INTERNAL_TRACE_MEMORY_ID(category, name);
+  base::trace_event::ScopedTraceMemory INTERNAL_TRACE_MEMORY_ID(category, name);
 #else
 #define INTERNAL_TRACE_MEMORY(category, name)
 #endif  // defined(TRACE_MEMORY_SUPPORTED)
diff --git a/base/trace_event/trace_event_memory_unittest.cc b/base/trace_event/trace_event_memory_unittest.cc
index 220c0e6..4732733 100644
--- a/base/trace_event/trace_event_memory_unittest.cc
+++ b/base/trace_event/trace_event_memory_unittest.cc
@@ -16,7 +16,7 @@
 #endif
 
 namespace base {
-namespace debug {
+namespace trace_event {
 
 // Tests for the trace event memory tracking system. Exists as a class so it
 // can be a friend of TraceMemoryController.
@@ -236,5 +236,5 @@ TEST_F(TraceMemoryTest, StringFromHexAddress) {
   EXPECT_STREQ(kHello, StringFromHexAddress(hex_address.str()));
 }
 
-}  // namespace debug
+}  // namespace trace_event
 }  // namespace base
diff --git a/base/trace_event/trace_event_synthetic_delay.cc b/base/trace_event/trace_event_synthetic_delay.cc
index 3651611..4b957c3 100644
--- a/base/trace_event/trace_event_synthetic_delay.cc
+++ b/base/trace_event/trace_event_synthetic_delay.cc
@@ -10,7 +10,7 @@ const int kMaxSyntheticDelays = 32;
 }  // namespace
 
 namespace base {
-namespace debug {
+namespace trace_event {
 
 TraceEventSyntheticDelayClock::TraceEventSyntheticDelayClock() {}
 TraceEventSyntheticDelayClock::~TraceEventSyntheticDelayClock() {}
@@ -200,7 +200,7 @@ void ResetTraceEventSyntheticDelays() {
   TraceEventSyntheticDelayRegistry::GetInstance()->ResetAllDelays();
 }
 
-}  // namespace debug
+}  // namespace trace_event
 }  // namespace base
 
 namespace trace_event_internal {
@@ -215,15 +215,16 @@ ScopedSyntheticDelay::~ScopedSyntheticDelay() {
   delay_impl_->EndParallel(end_time_);
 }
 
-base::debug::TraceEventSyntheticDelay* GetOrCreateDelay(
+base::trace_event::TraceEventSyntheticDelay* GetOrCreateDelay(
     const char* name,
     base::subtle::AtomicWord* impl_ptr) {
-  base::debug::TraceEventSyntheticDelay* delay_impl =
-      reinterpret_cast<base::debug::TraceEventSyntheticDelay*>(
+  base::trace_event::TraceEventSyntheticDelay* delay_impl =
+      reinterpret_cast<base::trace_event::TraceEventSyntheticDelay*>(
           base::subtle::Acquire_Load(impl_ptr));
   if (!delay_impl) {
-    delay_impl = base::debug::TraceEventSyntheticDelayRegistry::GetInstance()
-                     ->GetOrCreateDelay(name);
+    delay_impl =
+        base::trace_event::TraceEventSyntheticDelayRegistry::GetInstance()
+            ->GetOrCreateDelay(name);
     base::subtle::Release_Store(
         impl_ptr, reinterpret_cast<base::subtle::AtomicWord>(delay_impl));
   }
diff --git a/base/trace_event/trace_event_synthetic_delay.h b/base/trace_event/trace_event_synthetic_delay.h
index b52f3b0..14801be 100644
--- a/base/trace_event/trace_event_synthetic_delay.h
+++ b/base/trace_event/trace_event_synthetic_delay.h
@@ -65,7 +65,7 @@ template <typename Type>
 struct DefaultSingletonTraits;
 
 namespace base {
-namespace debug {
+namespace trace_event {
 
 // Time source for computing delay durations. Used for testing.
 class TRACE_EVENT_API_CLASS_EXPORT TraceEventSyntheticDelayClock {
@@ -138,7 +138,7 @@ class TRACE_EVENT_API_CLASS_EXPORT TraceEventSyntheticDelay {
 // Set the target durations of all registered synthetic delay points to zero.
 TRACE_EVENT_API_CLASS_EXPORT void ResetTraceEventSyntheticDelays();
 
-}  // namespace debug
+}  // namespace trace_event
 }  // namespace base
 
 namespace trace_event_internal {
@@ -151,14 +151,14 @@ class TRACE_EVENT_API_CLASS_EXPORT ScopedSyntheticDelay {
   ~ScopedSyntheticDelay();
 
  private:
-  base::debug::TraceEventSyntheticDelay* delay_impl_;
+  base::trace_event::TraceEventSyntheticDelay* delay_impl_;
   base::TimeTicks end_time_;
 
   DISALLOW_COPY_AND_ASSIGN(ScopedSyntheticDelay);
 };
 
 // Helper for registering delays. Do not use directly.
-TRACE_EVENT_API_CLASS_EXPORT base::debug::TraceEventSyntheticDelay*
+TRACE_EVENT_API_CLASS_EXPORT base::trace_event::TraceEventSyntheticDelay*
     GetOrCreateDelay(const char* name, base::subtle::AtomicWord* impl_ptr);
 
 }  // namespace trace_event_internal
diff --git a/base/trace_event/trace_event_synthetic_delay_unittest.cc b/base/trace_event/trace_event_synthetic_delay_unittest.cc
index 84ac75c..1dc0fc2 100644
--- a/base/trace_event/trace_event_synthetic_delay_unittest.cc
+++ b/base/trace_event/trace_event_synthetic_delay_unittest.cc
@@ -7,7 +7,7 @@
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
-namespace debug {
+namespace trace_event {
 namespace {
 
 const int kTargetDurationMs = 100;
@@ -150,5 +150,5 @@ TEST_F(TraceEventSyntheticDelayTest, BeginParallel) {
   EXPECT_LT((Now() - start_time).InMilliseconds(), kShortDurationMs);
 }
 
-}  // namespace debug
+}  // namespace trace_event
 }  // namespace base
diff --git a/base/trace_event/trace_event_system_stats_monitor.cc b/base/trace_event/trace_event_system_stats_monitor.cc
index 6fa0174..98f361a 100644
--- a/base/trace_event/trace_event_system_stats_monitor.cc
+++ b/base/trace_event/trace_event_system_stats_monitor.cc
@@ -16,13 +16,13 @@
 #include "base/trace_event/trace_event.h"
 
 namespace base {
-namespace debug {
+namespace trace_event {
 
 namespace {
 
 /////////////////////////////////////////////////////////////////////////////
 // Holds profiled system stats until the tracing system needs to serialize it.
-class SystemStatsHolder : public base::debug::ConvertableToTraceFormat {
+class SystemStatsHolder : public base::trace_event::ConvertableToTraceFormat {
  public:
   SystemStatsHolder() { }
 
@@ -30,7 +30,7 @@ class SystemStatsHolder : public base::debug::ConvertableToTraceFormat {
   // Uses the previous stats to compute rates if this is not the first profile.
   void GetSystemProfilingStats();
 
-  // base::debug::ConvertableToTraceFormat overrides:
+  // base::trace_event::ConvertableToTraceFormat overrides:
   void AppendAsTraceFormat(std::string* out) const override {
     AppendSystemProfileAsTraceFormat(system_stats_, out);
   }
@@ -129,5 +129,5 @@ void AppendSystemProfileAsTraceFormat(const SystemMetrics& system_metrics,
   *output += tmp;
 }
 
-}  // namespace debug
+}  // namespace trace_event
 }  // namespace base
diff --git a/base/trace_event/trace_event_system_stats_monitor.h b/base/trace_event/trace_event_system_stats_monitor.h
index 08fbfea..051669a 100644
--- a/base/trace_event/trace_event_system_stats_monitor.h
+++ b/base/trace_event/trace_event_system_stats_monitor.h
@@ -17,7 +17,7 @@ namespace base {
 
 class SingleThreadTaskRunner;
 
-namespace debug {
+namespace trace_event {
 
 // Watches for chrome://tracing to be enabled or disabled. When tracing is
 // enabled, also enables system events profiling. This class is the preferred
@@ -35,7 +35,7 @@ class BASE_EXPORT TraceEventSystemStatsMonitor
 
   virtual ~TraceEventSystemStatsMonitor();
 
-  // base::debug::TraceLog::EnabledStateChangedObserver overrides:
+  // base::trace_event::TraceLog::EnabledStateChangedObserver overrides:
   void OnTraceLogEnabled() override;
   void OnTraceLogDisabled() override;
 
@@ -69,7 +69,7 @@ BASE_EXPORT void AppendSystemProfileAsTraceFormat(const SystemMetrics&
                                                   system_stats,
                                                   std::string* output);
 
-}  // namespace debug
+}  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_TRACE_EVENT_SYSTEM_STATS_MONITOR_H_
diff --git a/base/trace_event/trace_event_system_stats_monitor_unittest.cc b/base/trace_event/trace_event_system_stats_monitor_unittest.cc
index 143ac4a..995f53b 100644
--- a/base/trace_event/trace_event_system_stats_monitor_unittest.cc
+++ b/base/trace_event/trace_event_system_stats_monitor_unittest.cc
@@ -12,7 +12,7 @@
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
-namespace debug {
+namespace trace_event {
 
 #if !defined(OS_IOS)
 // Tests for the system stats monitor.
@@ -62,5 +62,5 @@ TEST_F(TraceSystemStatsMonitorTest, TraceEventSystemStatsMonitor) {
 }
 #endif  // !defined(OS_IOS)
 
-}  // namespace debug
+}  // namespace trace_event
 }  // namespace base
diff --git a/base/trace_event/trace_event_unittest.cc b/base/trace_event/trace_event_unittest.cc
index 47b5ab6..a6bc0d4 100644
--- a/base/trace_event/trace_event_unittest.cc
+++ b/base/trace_event/trace_event_unittest.cc
@@ -25,7 +25,7 @@
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
-namespace debug {
+namespace trace_event {
 
 namespace {
 
@@ -3079,6 +3079,5 @@ TEST(TraceOptionsTest, TraceOptionsToString) {
   }
 }
 
-
-}  // namespace debug
+}  // namespace trace_event
 }  // namespace base
diff --git a/base/trace_event/trace_event_win.cc b/base/trace_event/trace_event_win.cc
index d2c3dc8..ebb55c8 100644
--- a/base/trace_event/trace_event_win.cc
+++ b/base/trace_event/trace_event_win.cc
@@ -9,7 +9,7 @@
 #include <initguid.h>  // NOLINT
 
 namespace base {
-namespace debug {
+namespace trace_event {
 
 using base::win::EtwEventType;
 using base::win::EtwMofEvent;
@@ -120,5 +120,5 @@ void TraceEventETWProvider::Resurrect() {
   StaticMemorySingletonTraits<TraceEventETWProvider>::Resurrect();
 }
 
-}  // namespace debug
+}  // namespace trace_event
 }  // namespace base
diff --git a/base/trace_event/trace_event_win.h b/base/trace_event/trace_event_win.h
index e447c35..dcb5aac 100644
--- a/base/trace_event/trace_event_win.h
+++ b/base/trace_event/trace_event_win.h
@@ -17,7 +17,7 @@ template <typename Type>
 struct StaticMemorySingletonTraits;
 
 namespace base {
-namespace debug {
+namespace trace_event {
 
 // This EtwTraceProvider subclass implements ETW logging
 // for the macros above on Windows.
@@ -119,6 +119,20 @@ enum TraceEventETWFlags {
 // Optionally the stack trace, consisting of a DWORD "depth", followed
 //    by an array of void* (machine bitness) of length "depth".
 
+}  // namespace trace_event
+}  // namespace base
+
+// TODO(ssid): remove these aliases after the tracing clients are moved to the
+// new trace_event namespace. See crbug.com/451032. ETA: March 2015.
+namespace base {
+namespace debug {
+using base::trace_event::kChromeTraceProviderName;
+using base::trace_event::kTraceEventClass32;
+using base::trace_event::kTraceEventClass64;
+using base::trace_event::kTraceEventTypeBegin;
+using base::trace_event::kTraceEventTypeEnd;
+using base::trace_event::kTraceEventTypeInstant;
+using base::trace_event::TraceEventETWProvider;
 }  // namespace debug
 }  // namespace base
 
diff --git a/base/trace_event/trace_event_win_unittest.cc b/base/trace_event/trace_event_win_unittest.cc
index a411301..7f1004e 100644
--- a/base/trace_event/trace_event_win_unittest.cc
+++ b/base/trace_event/trace_event_win_unittest.cc
@@ -20,7 +20,7 @@
 #include <initguid.h>  // NOLINT - must be last include.
 
 namespace base {
-namespace debug {
+namespace trace_event {
 
 namespace {
 
@@ -315,5 +315,5 @@ TEST_F(TraceEventWinTest, Macros) {
   PlayLog();
 }
 
-}  // namespace debug
+}  // namespace trace_event
 }  // namespace base