Deal with unhandled exceptions the same way in all Dart api functions.

runtime/bin/process.cc

Index: runtime/bin/process.cc
===================================================================
--- runtime/bin/process.cc	(revision 1469)
+++ runtime/bin/process.cc	(working copy)
@@ -34,11 +34,11 @@
   ASSERT(Dart_IsList(arguments));
   intptr_t length = 0;
   Dart_Handle result = Dart_ListLength(arguments, &length);
-  ASSERT(Dart_IsValid(result));
+  ASSERT(!Dart_IsError(result));
   char** string_args = new char*[length];
   for (int i = 0; i < length; i++) {
     Dart_Handle arg = Dart_ListGetAt(arguments, i);
-    ASSERT(Dart_IsValid(arg));
+    ASSERT(!Dart_IsError(arg));
     // The Dart code verifies that the arguments implement the String
     // interface. However, only builtin Strings are handled by
     // GetStringValue.