Fix up strings Sky passes to base/trace_event

sky/engine/core/frame/Tracing.cpp

 // Copyright 2015 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 "sky/engine/config.h"
 #include "sky/engine/core/frame/Tracing.h"
 
 #include "base/trace_event/trace_event.h"
 #include "sky/engine/wtf/text/StringUTF8Adaptor.h"
 
 namespace blink {
 
 Tracing::Tracing()
 {
 }
 
 Tracing::~Tracing()
 {
 }
 
 void Tracing::begin(const String& name)
 {
     StringUTF8Adaptor utf8(name);
-    TRACE_EVENT_COPY_BEGIN0("script", utf8.data());
+    // TRACE_EVENT_COPY_BEGIN0 needs a c-style null-terminated string.

[jamesr, 2015/04/29 00:12:46]

in particular, StringUTF8Adapter::data() doesn't return a pointer to a
null-terminated buffer

+    CString cstring(utf8.data(), utf8.length());

[jamesr, 2015/04/29 00:12:46]

this could be std::string as well. I figured CString is probably preferred here

+    TRACE_EVENT_COPY_BEGIN0("script", cstring.data());
 }
 
 void Tracing::end(const String& name)
 {
     StringUTF8Adaptor utf8(name);
-    TRACE_EVENT_COPY_END0("script", utf8.data());
+    // TRACE_EVENT_COPY_END0 needs a c-style null-terminated string.
+    CString cstring(utf8.data(), utf8.length());
+    TRACE_EVENT_COPY_END0("script", cstring.data());
 }
 
 } // namespace blink