Fix JNI NoSuchMethodErrors.

No point calling PrettyMethod if you've just determined that your Method* is
NULL...

Also a few other debugging aids.

Change-Id: I8af520716215800b7ffe4aef784b9c4ec15dcb92
diff --git a/src/stl_util.h b/src/stl_util.h
index 5fcf089..d826510 100644
--- a/src/stl_util.h
+++ b/src/stl_util.h
@@ -3,6 +3,8 @@
 #ifndef ART_SRC_STL_UTIL_H_
 #define ART_SRC_STL_UTIL_H_
 
+#include <iostream>
+
 namespace art {
 
 // STLDeleteContainerPointers()
@@ -54,6 +56,20 @@
   v->clear();
 }
 
+template <class T>
+std::string ToString(const T& v) {
+  std::stringstream os;
+  os << "[";
+  for (size_t i = 0; i < v.size(); ++i) {
+    os << v[i];
+    if (i < v.size() - 1) {
+      os << ", ";
+    }
+  }
+  os << "]";
+  return os.str();
+}
+
 }  // namespace art
 
 #endif  // ART_SRC_STL_UTIL_H_