Don't test directly against Scanner::kNoSourcePos instead use >= 0.

runtime/vm/flow_graph_compiler.cc

 // Copyright (c) 2013, 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/globals.h"  // Needed here to get TARGET_ARCH_XXX.
 
 #include "vm/flow_graph_compiler.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
@@ skipping 426 matching lines @@
   } else if (instr->MayThrow()  &&
              (CurrentTryIndex() != CatchClauseNode::kInvalidTryIndex)) {
     // Optimized try-block: Sync locals to fixed stack locations.
     EmitTrySync(instr, CurrentTryIndex());
   }
 }
 
 
 
 void FlowGraphCompiler::EmitSourceLine(Instruction* instr) {
-  if ((instr->token_pos() == Scanner::kNoSourcePos) || (instr->env() == NULL)) {
+  if ((instr->token_pos() < 0) || (instr->env() == NULL)) {
     return;
   }
   const Script& script =
       Script::Handle(zone(), instr->env()->function().script());
   intptr_t line_nr;
   intptr_t column_nr;
   script.GetTokenLocation(instr->token_pos(), &line_nr, &column_nr);
   const String& line = String::Handle(zone(), script.GetLine(line_nr));
   assembler()->Comment("Line %" Pd " in '%s':\n           %s",
       line_nr,
@@ skipping 1419 matching lines @@
 
 
 void FlowGraphCompiler::FrameStateClear() {
   ASSERT(!is_optimizing());
   frame_state_.TruncateTo(0);
 }
 #endif
 
 
 }  // namespace dart