initial import of Chrome's trace_event into skia framework

src/utils/SkEventTracer.cpp

+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkEventTracer.h"
+#include "SkOnce.h"
+
+class SkDefaultEventTracer: public SkEventTracer {
+    virtual SkEventTracer::Handle 
+        addTraceEvent(char phase,
+                      const uint8_t* categoryEnabledFlag,
+                      const char* name,
+                      uint64_t id,
+                      int numArgs,
+                      const char** argNames,
+                      const uint8_t* argTypes,
+                      const uint64_t* argValues,
+                      uint8_t flags) SK_OVERRIDE { return 0; }
+    
+    virtual void 
+        updateTraceEventDuration(const uint8_t* categoryEnabledFlag, 
+                                 const char* name, 
+                                 SkEventTracer::Handle) SK_OVERRIDE {};
+
+    virtual const uint8_t* getCategoryGroupEnabled(const char* name) SK_OVERRIDE {
+        static uint8_t no = 0;
+        return &no;
+    };
+    virtual const char* getCategoryGroupName(
+      const uint8_t* category_group_enabled) SK_OVERRIDE {
+        static const char* dummy = "dummy";
+        return dummy;
+    };
+};
+
+SkEventTracer *SkEventTracer::gInstance;
+
+static void intiailize_default_tracer(int) {
+    SkEventTracer::SetInstance(SkNEW(SkDefaultEventTracer));
+}
+
+static void cleanup_tracer() {
+    // calling SetInstance will delete the existing instance.
+    SkEventTracer::SetInstance(NULL);
+}
+
+SkEventTracer* SkEventTracer::GetInstance() {
+    SK_DECLARE_STATIC_ONCE(once);
+    SkOnce(&once, intiailize_default_tracer, 0, cleanup_tracer);
+    SkASSERT(NULL != SkEventTracer::gInstance);
+    return SkEventTracer::gInstance;
+}