Add optional message argument to assert statements in the VM.

runtime/lib/errors.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/bootstrap_natives.h"
 #include "vm/exceptions.h"
 #include "vm/object_store.h"
 #include "vm/runtime_entry.h"
 #include "vm/stack_frame.h"
 
 namespace dart {
 
 // Allocate and throw a new AssertionError.
 // Arg0: index of the first token of the failed assertion.
 // Arg1: index of the first token after the failed assertion.
 // Return value: none, throws an exception.
-DEFINE_NATIVE_ENTRY(AssertionError_throwNew, 2) {
+DEFINE_NATIVE_ENTRY(AssertionError_throwNew, 3) {
   // No need to type check the arguments. This function can only be called
   // internally from the VM.
   intptr_t assertion_start =
       Smi::CheckedHandle(arguments->NativeArgAt(0)).Value();
   intptr_t assertion_end =
       Smi::CheckedHandle(arguments->NativeArgAt(1)).Value();
-
-  const Array& args = Array::Handle(Array::New(4));
+  const Instance& message = Instance::CheckedHandle(arguments->NativeArgAt(2));
+  const Array& args = Array::Handle(Array::New(5));
 
   DartFrameIterator iterator;
   iterator.NextFrame();  // Skip native call.
   const Script& script = Script::Handle(Exceptions::GetCallerScript(&iterator));
 
   // Initialize argument 'failed_assertion' with source snippet.
   intptr_t from_line, from_column;
   script.GetTokenLocation(assertion_start, &from_line, &from_column);
   intptr_t to_line, to_column;
   script.GetTokenLocation(assertion_end, &to_line, &to_column);
   // The snippet will extract the correct assertion code even if the source
   // is generated.
   args.SetAt(0, String::Handle(
       script.GetSnippet(from_line, from_column, to_line, to_column)));
 
   // Initialize location arguments starting at position 1.
   // Do not set a column if the source has been generated as it will be wrong.
   args.SetAt(1, String::Handle(script.url()));
   args.SetAt(2, Smi::Handle(Smi::New(from_line)));
   args.SetAt(3, Smi::Handle(Smi::New(script.HasSource() ? from_column : -1)));
+  args.SetAt(4, message);
 
   Exceptions::ThrowByType(Exceptions::kAssertion, args);
   UNREACHABLE();
   return Object::null();
 }
 
 
 // Allocate and throw a new TypeError or CastError.
 // Arg0: index of the token of the failed type check.
 // Arg1: src value.
@@ skipping 64 matching lines @@
   intptr_t line;
   script.GetTokenLocation(error_pos, &line, NULL);
   args.SetAt(2, Smi::Handle(Smi::New(line)));
 
   Exceptions::ThrowByType(Exceptions::kAbstractClassInstantiation, args);
   UNREACHABLE();
   return Object::null();
 }
 
 }  // namespace dart