Finish file 'fuzzer' and fix issues.

runtime/bin/dartutils.h

Index: runtime/bin/dartutils.h
diff --git a/runtime/bin/dartutils.h b/runtime/bin/dartutils.h
index 9f756bb8d9bb6203f5e5e96cbbd8e9c5afaf841a..a645d698a909d77690efe49f14e429c6fa2884d2 100644
--- a/runtime/bin/dartutils.h
+++ b/runtime/bin/dartutils.h
@@ -59,7 +59,14 @@ class DartUtils {
  public:
   // TODO(turnidge): Clean up the implementations of these so that
   // they allow for proper error propagation.
+
+  // Assumes that the value object is known to be an integer object
+  // that fits in a signed 64-bit integer.
   static int64_t GetIntegerValue(Dart_Handle value_obj);
+  // Checks that the value object is an integer object that fits in a
+  // signed 64-bit integer. If it is, the value is returned in the
+  // value out parameter and true is returned. Otherwise, false is
+  // returned.
   static bool GetInt64Value(Dart_Handle value_obj, int64_t* value);
   static const char* GetStringValue(Dart_Handle str_obj);
   static bool GetBooleanValue(Dart_Handle bool_obj);