Added a bionic systrace class and tracing to pthread_mutex.cpp.

bionic_systrace.h contains an implementation of tracing that
can be used with systrace.py and its associated viewer.  pthread_mutex
now uses this tracing to track pthread_mutex contention, which can be
enabled by using the "bionic" command line option to systrace.

Bug: 15116468

(cherry picked from commit a406ee6d5f)

Change-Id: Ic98fc303689fe9384974150d0d258c50806a55e4

libc/private/bionic_systrace.h

@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef BIONIC_SYSTRACE_H
+#define BIONIC_SYSTRACE_H
+
+#include "bionic_macros.h"
+
+// Tracing class for bionic. To begin a trace at a specified point:
+//   ScopedTrace("Trace message");
+// The trace will end when the contructor goes out of scope.
+
+class ScopedTrace {
+ public:
+  explicit ScopedTrace(const char* message);
+  ~ScopedTrace();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ScopedTrace);
+};
+
+#endif