Use zone memory for StackTrace::ToCString.

runtime/vm/zone_text_buffer.h

Index: runtime/vm/zone_text_buffer.h
diff --git a/runtime/vm/zone_text_buffer.h b/runtime/vm/zone_text_buffer.h
new file mode 100644
index 0000000000000000000000000000000000000000..28a39eb529f8aaddf0048696beefd5af584d827d
--- /dev/null
+++ b/runtime/vm/zone_text_buffer.h
@@ -0,0 +1,38 @@
+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file

[zra, 2017/02/09 20:37:48]

2017

[rmacnak, 2017/02/11 01:44:12]

Fixed in https://codereview.chromium.org/2686813006

+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#ifndef RUNTIME_VM_ZONE_TEXT_BUFFER_H_
+#define RUNTIME_VM_ZONE_TEXT_BUFFER_H_
+
+#include "vm/allocation.h"
+#include "vm/globals.h"
+
+namespace dart {
+
+class Zone;
+
+// TextBuffer maintains a dynamic character buffer with a printf-style way to
+// append text.
+class ZoneTextBuffer : ValueObject {
+ public:
+  ZoneTextBuffer(Zone* zone, intptr_t initial_capacity);
+  ~ZoneTextBuffer() {}
+
+  intptr_t Printf(const char* format, ...) PRINTF_ATTRIBUTE(2, 3);
+  void AddString(const char* s);
+
+  char* buffer() { return buffer_; }
+  intptr_t length() { return length_; }
+
+ private:
+  void EnsureCapacity(intptr_t len);
+  Zone* zone_;
+  char* buffer_;
+  intptr_t length_;
+  intptr_t capacity_;
+};
+
+}  // namespace dart
+
+#endif  // RUNTIME_VM_ZONE_TEXT_BUFFER_H_