Add perf test configuration to track memory use of context and isolate.

tools/run_perf.py

 #!/usr/bin/env python
 # Copyright 2014 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """
 Performance runner for d8.
 
 Call e.g. with tools/run-perf.py --arch ia32 some_suite.json
 
@@ skipping 393 matching lines @@
           trace_result.traces[0]["stddev"] = stddev
 
     return reduce(lambda r, t: r + t, traces.itervalues(), Results())
 
 
 def MakeGraph(suite, arch, parent):
   """Factory method for making graph objects."""
   if isinstance(parent, Runnable):
     # Below a runnable can only be traces.
     return Trace(suite, parent, arch)
-  elif suite.get("main"):
-    # A main file makes this graph runnable.
+  elif suite.get("main") is not None:
+    # A main file makes this graph runnable. Empty strings are accepted.
     if suite.get("tests"):
       # This graph has subgraphs (traces).
       return Runnable(suite, parent, arch)
     else:
       # This graph has no subgraphs, it's a leaf.
       return RunnableTrace(suite, parent, arch)
   elif suite.get("generic"):
     # This is a generic suite definition. It is either a runnable executable
     # or has a main js file.
     return RunnableGeneric(suite, parent, arch)
@@ skipping 285 matching lines @@
 
   if options.json_test_results:
     results.WriteToFile(options.json_test_results)
   else:  # pragma: no cover
     print results
 
   return min(1, len(results.errors))
 
 if __name__ == "__main__":  # pragma: no cover
   sys.exit(Main(sys.argv[1:]))