Fix Dart_GlobalTimelineGetTrace to null terminate the string

runtime/vm/dart_api_impl.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // 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.
 
 #include "include/dart_api.h"
 #include "include/dart_mirrors_api.h"
 #include "include/dart_native_api.h"
 
 #include "platform/assert.h"
 #include "vm/class_finalizer.h"
@@ skipping 5788 matching lines @@
 
 
 static bool StreamTraceEvents(Dart_StreamConsumer consumer,
                               void* user_data,
                               JSONStream* js) {
   ASSERT(js != NULL);
   // Steal output from JSONStream.
   char* output = NULL;
   intptr_t output_length = 0;
   js->Steal(const_cast<const char**>(&output), &output_length);
+  if (output_length < 3) {
+    // Empty JSON array.
+    free(output);
+    return false;
+  }
+  // We want to send the JSON array without the leading '[' or trailing ']'
+  // characters.
+  ASSERT(output[0] == '[');
+  ASSERT(output[output_length - 1] == ']');
+  // Replace the ']' with the null character.
+  output[output_length - 1] = '\0';
+  // We are skipping the '['.
+  output_length -= 1;
 
   // Start the stream.
   StartStreamToConsumer(consumer, user_data, "timeline");
 
   DataStreamToConsumer(consumer,
                        user_data,
-                       output,
+                       &output[1],
                        output_length,
                        "timeline");
 
   // We stole the JSONStream's output buffer, free it.
   free(output);
 
   // Finish the stream.
   FinishStreamToConsumer(consumer, user_data, "timeline");
   return true;
 }
@@ skipping 205 matching lines @@
                                    ApiReallocate);
   writer.WriteFullSnapshot();
   *vm_isolate_snapshot_size = writer.VmIsolateSnapshotSize();
   *isolate_snapshot_size = writer.IsolateSnapshotSize();
   *instructions_snapshot_size = writer.InstructionsSnapshotSize();
 
   return Api::Success();
 }
 
 }  // namespace dart