Fix clang based build after r40969.

runtime/vm/flow_graph_range_analysis.cc

 // Copyright (c) 2014, 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/flow_graph_range_analysis.h"
 
 #include "vm/bit_vector.h"
 #include "vm/il_printer.h"
 
 namespace dart {
@@ skipping 110 matching lines @@
       limit = constraint;
     }
   }
 
   return limit;
 }
 
 
 static InductionVariableInfo* DetectSimpleInductionVariable(PhiInstr* phi) {
   if (phi->Type()->ToCid() != kSmiCid) {
-    return false;
+    return NULL;
   }
 
   if (phi->InputCount() != 2) {
-    return false;
+    return NULL;
   }
 
   BitVector* loop_info = phi->block()->loop_info();
 
   const intptr_t backedge_idx =
       loop_info->Contains(phi->block()->PredecessorAt(0)->preorder_number())
           ? 0 : 1;
 
   Definition* initial_value =
       phi->InputAt(1 - backedge_idx)->definition();
@@ skipping 2893 matching lines @@
     }
   } while (CanonicalizeMaxBoundary(&max) ||
            CanonicalizeMinBoundary(&canonical_length));
 
   // Failed to prove that maximum is bounded with array length.
   return false;
 }
 
 
 }  // namespace dart