Move a definition to fix a compiler error

runtime/vm/kernel.h

 // Copyright (c) 2016, 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 RUNTIME_VM_KERNEL_H_
 #define RUNTIME_VM_KERNEL_H_
 
 #if !defined(DART_PRECOMPILED_RUNTIME)
 #include "platform/assert.h"
 #include "vm/allocation.h"
@@ skipping 917 matching lines @@
   AsyncMarker dart_async_marker() { return dart_async_marker_; }
   TypeParameterList& type_parameters() { return type_parameters_; }
   int required_parameter_count() { return required_parameter_count_; }
   List<VariableDeclaration>& positional_parameters() {
     return positional_parameters_;
   }
   List<VariableDeclaration>& named_parameters() { return named_parameters_; }
   DartType* return_type() { return return_type_; }
 
   Statement* body() { return body_; }
-  void ReplaceBody(Statement* body) {
-    delete body_;
-    // Use static_cast to invoke the conversion function and so avoid triggering
-    // ASSERT(pointer_ == NULL) in operator= when overwriting a non-NULL body.
-    static_cast<Statement*&>(body_) = body;
-  }
+  void ReplaceBody(Statement* body);
 
   TokenPosition position() { return position_; }
   TokenPosition end_position() { return end_position_; }
 
  private:
   FunctionNode()
       : position_(TokenPosition::kNoSource),
         end_position_(TokenPosition::kNoSource) {}
 
   AsyncMarker async_marker_;
@@ skipping 2387 matching lines @@
 }  // namespace kernel
 
 kernel::Program* ReadPrecompiledKernelFromBuffer(const uint8_t* buffer,
                                                  intptr_t buffer_length);
 
 
 }  // namespace dart
 
 #endif  // !defined(DART_PRECOMPILED_RUNTIME)
 #endif  // RUNTIME_VM_KERNEL_H_