Generate dynamic type errors according to spec.

runtime/vm/parser.h

Index: runtime/vm/parser.h
===================================================================
--- runtime/vm/parser.h	(revision 5063)
+++ runtime/vm/parser.h	(working copy)
@@ -89,6 +89,14 @@
                                const char* format,
                                va_list args);
 
+  // Same as FormatError, but appends the new error to the 'prev_error'.
+  static RawError* FormatErrorWithAppend(const Error& prev_error,
+                                         const Script& script,
+                                         intptr_t token_index,
+                                         const char* message_header,
+                                         const char* format,
+                                         va_list args);
+
  private:
   struct Block;
   class TryBlocks;
@@ -192,18 +200,14 @@
   // Reports error message at given location.
   void ErrorMsg(intptr_t token_index, const char* msg, ...);
   void Warning(intptr_t token_index, const char* msg, ...);
+
+  // Reports an already formatted error message.
+  void ErrorMsg(const Error& error);
+
   // Concatenates two error messages, the previous and the current one.
   void AppendErrorMsg(
       const Error& prev_error, intptr_t token_index, const char* format, ...);
 
-  // Same as FormatError, but appends the new error to the 'prev_error'.
-  static RawError* FormatErrorWithAppend(const Error& prev_error,
-                                         const Script& script,
-                                         intptr_t token_index,
-                                         const char* message_header,
-                                         const char* format,
-                                         va_list args);
-
   const Instance& EvaluateConstExpr(AstNode* expr);
   void RunStaticFieldInitializer(const Field& field);
   RawObject* EvaluateConstConstructorCall(