bpf_dsl: move more implementation details out of bpf_dsl.h

sandbox/linux/bpf_dsl/bpf_dsl_impl.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SANDBOX_LINUX_BPF_DSL_BPF_DSL_IMPL_H_
 #define SANDBOX_LINUX_BPF_DSL_BPF_DSL_IMPL_H_
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "sandbox/sandbox_export.h"
 
 namespace sandbox {
 class ErrorCode;
-class SandboxBPF;
 
 namespace bpf_dsl {
+class PolicyCompiler;
+
 namespace internal {
 
 // Internal interface implemented by BoolExpr implementations.
 class BoolExprImpl : public base::RefCounted<BoolExprImpl> {
  public:
-  BoolExprImpl() {}
+  // Compile uses |pc| to construct an ErrorCode that conditionally continues
+  // to either |true_ec| or |false_ec|, depending on whether the represented
+  // boolean expression is true or false.
   virtual ErrorCode Compile(PolicyCompiler* pc,
                             ErrorCode true_ec,
                             ErrorCode false_ec) const = 0;
 
  protected:
+  BoolExprImpl() {}
   virtual ~BoolExprImpl() {}
 
  private:
   friend class base::RefCounted<BoolExprImpl>;
   DISALLOW_COPY_AND_ASSIGN(BoolExprImpl);
 };
 
 // Internal interface implemented by ResultExpr implementations.
 class ResultExprImpl : public base::RefCounted<ResultExprImpl> {
  public:
-  ResultExprImpl() {}
+  // Compile uses |pc| to construct an ErrorCode analogous to the represented
+  // result expression.
   virtual ErrorCode Compile(PolicyCompiler* pc) const = 0;
+
+  // HasUnsafeTraps returns whether the result expression is or recursively
+  // contains an unsafe trap expression.
   virtual bool HasUnsafeTraps() const;
 
  protected:
+  ResultExprImpl() {}
   virtual ~ResultExprImpl() {}
 
  private:
   friend class base::RefCounted<ResultExprImpl>;
   DISALLOW_COPY_AND_ASSIGN(ResultExprImpl);
 };
 
 }  // namespace internal
 }  // namespace bpf_dsl
 }  // namespace sandbox
 
 #endif  // SANDBOX_LINUX_BPF_DSL_BPF_DSL_IMPL_H_