Make the "sticky error" an Error instead of a String.

runtime/vm/parser.h

 // Copyright (c) 2011, 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.
 
 #ifndef VM_PARSER_H_
 #define VM_PARSER_H_
 
 #include "include/dart_api.h"
 
 #include "vm/ast.h"
@@ skipping 62 matching lines @@
          const Function& function,
          intptr_t token_index);
 
   // Parse the top level of a whole script file and register declared classes
   // and interfaces in the given library.
   static void ParseCompilationUnit(const Library& library,
                                    const Script& script);
 
   static void ParseFunction(ParsedFunction* parsed_function);
 
-  // Format an error or warning message into the message_buffer.
+  // Build an error object containing a formatted error or warning message.
   // A null script means no source and a negative token_index means no position.
-  static void FormatMessage(const Script& script,
-                            intptr_t token_index,
-                            const char* message_header,
-                            char* message_buffer,
-                            intptr_t message_buffer_size,
-                            const char* format,
-                            va_list args);
+  static RawError* FormatError(const Script& script,
+                               intptr_t token_index,
+                               const char* message_header,
+                               const char* format,
+                               va_list args);
 
  private:
   struct Block;
   class TryBlocks;
 
   // The function being parsed.
   const Function& current_function() const;
 
   // Note that a local function may be parsed multiple times. It is first parsed
   // when its outermost enclosing function is being parsed. It is then parsed
@@ skipping 62 matching lines @@
   void SkipMapLiteral();
   void SkipListLiteral();
   void SkipFunctionLiteral();
   void SkipStringLiteral();
 
   void CheckConstructorCallTypeArguments(
     intptr_t pos,
     Function& constructor,
     const AbstractTypeArguments& type_arguments);
 
+  // Format an error or warning message into the message_buffer.
+  // A null script means no source and a negative token_index means no position.
+  static void FormatMessage(const Script& script,
+                            intptr_t token_index,
+                            const char* message_header,
+                            char* message_buffer,
+                            intptr_t message_buffer_size,
+                            const char* format,
+                            va_list args);
+
   // Reports error message at location of current token.
   void ErrorMsg(const char* msg, ...);
   void ErrorMsg(intptr_t token_index, const char* msg, ...);
   void Warning(const char* msg, ...);
   void Warning(intptr_t token_index, const char* msg, ...);
   void Unimplemented(const char* msg);
 
   const Instance& EvaluateConstExpr(AstNode* expr);
   void RunStaticFieldInitializer(const Field& field);
   RawInstance* EvaluateConstConstructorCall(
@@ skipping 265 matching lines @@
   // code at all points in the try block where an exit from the block is
   // done using 'return', 'break' or 'continue' statements.
   TryBlocks* try_blocks_list_;
 
   DISALLOW_COPY_AND_ASSIGN(Parser);
 };
 
 }  // namespace dart
 
 #endif  // VM_PARSER_H_