Reduce snapshot size by not writing null values for function code fields.

runtime/vm/raw_object.h

 // 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.
 
 #ifndef VM_RAW_OBJECT_H_
 #define VM_RAW_OBJECT_H_
 
 #include "platform/assert.h"
 #include "vm/globals.h"
 #include "vm/token.h"
@@ skipping 602 matching lines @@
   RawArray* parameter_names_;
   RawObject* data_;  // Additional data specific to the function kind.
   RawInstructions* instructions_;  // Instructions of currently active code.
   RawCode* unoptimized_code_;  // Unoptimized code, keep it after optimization.
   RawObject** to() {
     return reinterpret_cast<RawObject**>(&ptr()->unoptimized_code_);
   }
   RawObject** to_no_code() {
     return reinterpret_cast<RawObject**>(&ptr()->data_);
   }
+  RawObject** to_snapshot() {
+    return reinterpret_cast<RawObject**>(&ptr()->data_);
+  }
 
   intptr_t token_pos_;
   intptr_t end_token_pos_;
   intptr_t usage_counter_;  // Incremented while function is running.
   int16_t num_fixed_parameters_;
   int16_t num_optional_parameters_;  // > 0: positional; < 0: named.
   int16_t deoptimization_counter_;
   uint16_t kind_tag_;  // See Function::KindTagBits.
   uint16_t optimized_instruction_count_;
   uint16_t optimized_call_site_count_;
@@ skipping 1223 matching lines @@
   COMPILE_ASSERT(kTypedDataInt8ArrayViewCid == kTypedDataInt8ArrayCid + 14);
   COMPILE_ASSERT(kExternalTypedDataInt8ArrayCid ==
                  kTypedDataInt8ArrayViewCid + 15);
   COMPILE_ASSERT(kNullCid == kExternalTypedDataInt8ArrayCid + 14);
   return (kNullCid - kTypedDataInt8ArrayCid);
 }
 
 }  // namespace dart
 
 #endif  // VM_RAW_OBJECT_H_