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

runtime/vm/flow_graph_compiler_x64.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_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/flow_graph_compiler.h"
 
 #include "vm/ast_printer.h"
@@ skipping 1392 matching lines @@
   }
 
   if (needs_number_check) {
     __ pushq(reg);
     __ PushObject(obj);
     if (is_optimizing()) {
       __ CallPatchable(*StubCode::OptimizedIdenticalWithNumberCheck_entry());
     } else {
       __ CallPatchable(*StubCode::UnoptimizedIdenticalWithNumberCheck_entry());
     }
-    if (token_pos != Scanner::kNoSourcePos) {
+    if (token_pos >= 0) {
       AddCurrentDescriptor(RawPcDescriptors::kRuntimeCall,
                            Thread::kNoDeoptId,
                            token_pos);
     }
     // Stub returns result in flags (result of a cmpq, we need ZF computed).
     __ popq(reg);  // Discard constant.
     __ popq(reg);  // Restore 'reg'.
   } else {
     __ CompareObject(reg, obj);
   }
   return EQUAL;
 }
 
 
 Condition FlowGraphCompiler::EmitEqualityRegRegCompare(Register left,
                                                        Register right,
                                                        bool needs_number_check,
                                                        intptr_t token_pos) {
   if (needs_number_check) {
     __ pushq(left);
     __ pushq(right);
     if (is_optimizing()) {
       __ CallPatchable(*StubCode::OptimizedIdenticalWithNumberCheck_entry());
     } else {
       __ CallPatchable(*StubCode::UnoptimizedIdenticalWithNumberCheck_entry());
     }
-    if (token_pos != Scanner::kNoSourcePos) {
+    if (token_pos >= 0) {
       AddCurrentDescriptor(RawPcDescriptors::kRuntimeCall,
                            Thread::kNoDeoptId,
                            token_pos);
     }
     // Stub returns result in flags (result of a cmpq, we need ZF computed).
     __ popq(right);
     __ popq(left);
   } else {
     __ cmpl(left, right);
   }
@@ skipping 360 matching lines @@
   __ movups(reg, Address(RSP, 0));
   __ AddImmediate(RSP, Immediate(kFpuRegisterSize));
 }
 
 
 #undef __
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64