Fix gcc 4.9 build errors.

runtime/vm/compiler.cc

 // Copyright (c) 2012, 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/compiler.h"
 
 #include "vm/assembler.h"
 
 #include "vm/ast_printer.h"
 #include "vm/block_scheduler.h"
@@ skipping 1476 matching lines @@
   UNREACHABLE();
   return Error::null();
 }
 
 
 void Compiler::ComputeLocalVarDescriptors(const Code& code) {
   ASSERT(!code.is_optimized());
   const Function& function = Function::Handle(code.function());
   ParsedFunction* parsed_function = new ParsedFunction(
       Thread::Current(), Function::ZoneHandle(function.raw()));
-  LocalVarDescriptors& var_descs =
-      LocalVarDescriptors::Handle(code.var_descriptors());
-  ASSERT(var_descs.IsNull());
+  ASSERT(code.var_descriptors() == Object::null());
   // IsIrregexpFunction have eager var descriptors generation.
   ASSERT(!function.IsIrregexpFunction());
   // In background compilation, parser can produce 'errors": bailouts
   // if state changed while compiling in background.
   LongJumpScope jump;
   if (setjmp(*jump.Set()) == 0) {
     Parser::ParseFunction(parsed_function);
     parsed_function->AllocateVariables();
-    var_descs = parsed_function->node_sequence()->scope()->
-        GetVarDescriptors(function);
+    const LocalVarDescriptors& var_descs = LocalVarDescriptors::Handle(
+        parsed_function->node_sequence()->scope()->GetVarDescriptors(function));
     ASSERT(!var_descs.IsNull());
     code.set_var_descriptors(var_descs);
   } else {
     // Only possible with background compilation.
     ASSERT(Compiler::IsBackgroundCompilation());
   }
 }
 
 
 RawError* Compiler::CompileAllFunctions(const Class& cls) {
@@ skipping 585 matching lines @@
 }
 
 
 void BackgroundCompiler::EnsureInit(Thread* thread) {
   UNREACHABLE();
 }
 
 #endif  // DART_PRECOMPILED_RUNTIME
 
 }  // namespace dart