Add optional message argument to assert statements in the VM.

runtime/vm/parser.h

Index: runtime/vm/parser.h
diff --git a/runtime/vm/parser.h b/runtime/vm/parser.h
index ece272949ccec809dd1b83eb9ede6f3e32515ac2..7cbcf8790e5c2a853827375c9a6e9810eef6ac50 100644
--- a/runtime/vm/parser.h
+++ b/runtime/vm/parser.h
@@ -782,7 +782,7 @@ class Parser : public ValueObject {
                           const String& func_name,
                           ArgumentListNode* arguments);
   String& Interpolate(const GrowableArray<AstNode*>& values);
-  AstNode* MakeAssertCall(intptr_t begin, intptr_t end);
+  AstNode* MakeAssertCall(intptr_t begin, intptr_t end, AstNode* message);
   AstNode* ThrowTypeError(intptr_t type_pos, const AbstractType& type,
                            LibraryPrefix* prefix = NULL);
   AstNode* ThrowNoSuchMethodError(intptr_t call_pos,