Added support to trace_event for passing static string arguments without copy

base/debug/trace_event_unittest.cc

Index: base/debug/trace_event_unittest.cc
diff --git a/base/debug/trace_event_unittest.cc b/base/debug/trace_event_unittest.cc
index 7217b1dee839010667d3580ff752ad0ad99ff1e9..9e934c939baa1d1653e162909fb1a0c1db8f3791 100644
--- a/base/debug/trace_event_unittest.cc
+++ b/base/debug/trace_event_unittest.cc
@@ -8,6 +8,7 @@
 #include "base/command_line.h"
 #include "base/json/json_reader.h"
 #include "base/json/json_writer.h"
+#include "base/memory/ref_counted_memory.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/process_util.h"
 #include "base/stringprintf.h"
@@ -462,6 +463,41 @@ TEST_F(TraceEventTestFixture, DataCapturedThreshold) {
   EXPECT_NOT_FIND_BE_("4thresholdlong2");
 }
 
+// Test that static strings are not copied.
+TEST_F(TraceEventTestFixture, StaticStringVsString) {
+  ManualTestSetUp();
+  TraceLog* tracer = TraceLog::GetInstance();
+  // Make sure old events are flushed:
+  tracer->SetEnabled(false);
+  EXPECT_EQ(0u, tracer->GetEventsSize());
+
+  {
+    // Test that normal string arguments are copied.
+    tracer->SetEnabled(true);
+    TRACE_EVENT2("cat", "name1", "arg1", "argval", "arg2", "argval");
+    size_t num_events = tracer->GetEventsSize();
+    EXPECT_GT(num_events, 0u);
+    const TraceEvent& event = tracer->GetEventAt(num_events - 1);
+    EXPECT_STREQ("name1", event.name());
+    EXPECT_TRUE(event.parameter_copy_storage() != NULL);
+    EXPECT_GT(event.parameter_copy_storage()->size(), 0u);
+    tracer->SetEnabled(false);
+  }
+
+  {
+    // Test that static string arguments are not copied.
+    tracer->SetEnabled(true);
+    TRACE_EVENT2("cat", "name2", "arg1", TRACE_STATIC_STR("argval"),
+                 "arg2", TRACE_STATIC_STR("argval"));
+    size_t num_events = tracer->GetEventsSize();
+    EXPECT_GT(num_events, 0u);
+    const TraceEvent& event = tracer->GetEventAt(num_events - 1);
+    EXPECT_STREQ("name2", event.name());
+    EXPECT_TRUE(event.parameter_copy_storage() == NULL);
+    tracer->SetEnabled(false);
+  }
+}
+
 // Test that data sent from other threads is gathered
 TEST_F(TraceEventTestFixture, DataCapturedOnThread) {
   ManualTestSetUp();