ART: dex2oat flag for HGraphVisualizer dump file

This patch adds a new '--dump-cfg=<file>' flag to dex2oat which
specifies the file that HGraphVisualizer will store its output into.
Until now the graph was dumped to 'art.cfg' in the current working
directory. To make Checker work with run-test, the output directory
needs to be customizable.

Change-Id: I4a940f7708b88deea5a0e51d13aed13e52199349
diff --git a/compiler/common_compiler_test.cc b/compiler/common_compiler_test.cc
index 7df71f5..96f8e0c 100644
--- a/compiler/common_compiler_test.cc
+++ b/compiler/common_compiler_test.cc
@@ -164,7 +164,7 @@
                                               compiler_kind, instruction_set,
                                               instruction_set_features_.get(),
                                               true, new std::set<std::string>, nullptr,
-                                              2, true, true, timer_.get(), -1, ""));
+                                              2, true, true, "", timer_.get(), -1, ""));
   }
   // We typically don't generate an image in unit tests, disable this optimization by default.
   compiler_driver_->SetSupportBootImageFixup(false);