Migrate most uses of Isolate::current_zone to Thread::zone.

runtime/vm/json_stream.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 "platform/assert.h"
 
 #include "vm/dart_entry.h"
 #include "vm/debugger.h"
 #include "vm/json_stream.h"
 #include "vm/message.h"
@@ skipping 113 matching lines @@
 void JSONStream::PrintError(intptr_t code,
                             const char* details_format, ...) {
   SetupError();
   JSONObject jsobj(this);
   jsobj.AddProperty("code", code);
   jsobj.AddProperty("message", GetJSONRpcErrorMessage(code));
   {
     JSONObject data(&jsobj, "data");
     PrintRequest(&data, this);
     if (details_format != NULL) {
-      Isolate* isolate = Isolate::Current();
-
       va_list args;
       va_start(args, details_format);
       intptr_t len = OS::VSNPrint(NULL, 0, details_format, args);
       va_end(args);
 
-      char* buffer = isolate->current_zone()->Alloc<char>(len + 1);
+      char* buffer = Thread::Current()->zone()->Alloc<char>(len + 1);
       va_list args2;
       va_start(args2, details_format);
       OS::VSNPrint(buffer, (len + 1), details_format, args2);
       va_end(args2);
 
       data.AddProperty("details", buffer);
     }
   }
 }
 
@@ skipping 527 matching lines @@
   intptr_t len2 = OS::VSNPrint(p, len+1, format, args);
   va_end(args);
   ASSERT(len == len2);
   stream_->buffer_.AddChar('"');
   stream_->AddEscapedUTF8String(p);
   stream_->buffer_.AddChar('"');
   free(p);
 }
 
 }  // namespace dart