Fix precompile build issue with IsString change.

runtime/vm/precompiler.cc

 // Copyright (c) 2015, 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/precompiler.h"
 
 #include "vm/aot_optimizer.h"
 #include "vm/assembler.h"
 #include "vm/ast_printer.h"
 #include "vm/branch_optimizer.h"
@@ skipping 211 matching lines @@
     DedupStackmapLists();
 
     if (FLAG_dedup_instructions) {
       // Reduces binary size but obfuscates profiler results.
       DedupInstructions();
     }
 
     zone_ = NULL;
   }
 
-  // TODO(rmacnak): intptr_t dropped_symbols_count = Symbols::Compact(I);
-  intptr_t dropped_symbols_count = 0;
-
+  intptr_t dropped_symbols_count = Symbols::Compact(I);
   if (FLAG_trace_precompiler) {
     THR_Print("Precompiled %" Pd " functions,", function_count_);
     THR_Print(" %" Pd " dynamic types,", class_count_);
     THR_Print(" %" Pd " dynamic selectors.\n", selector_count_);
 
     THR_Print("Dropped %" Pd " functions,", dropped_function_count_);
     THR_Print(" %" Pd " fields,", dropped_field_count_);
     THR_Print(" %" Pd " symbols,", dropped_symbols_count);
     THR_Print(" %" Pd " types,", dropped_type_count_);
     THR_Print(" %" Pd " type arguments,", dropped_typearg_count_);
@@ skipping 2506 matching lines @@
       CompilationPipeline::New(thread->zone(), function);
 
   ASSERT(FLAG_precompiled_mode);
   const bool optimized = function.IsOptimizable();  // False for natives.
   return PrecompileFunctionHelper(pipeline, function, optimized);
 }
 
 #endif  // DART_PRECOMPILER
 
 }  // namespace dart