sandbox_bpf: rework how unsafe traps are compiled/verified

sandbox/linux/bpf_dsl/bpf_dsl.h

Index: sandbox/linux/bpf_dsl/bpf_dsl.h
diff --git a/sandbox/linux/bpf_dsl/bpf_dsl.h b/sandbox/linux/bpf_dsl/bpf_dsl.h
index 7bb691305ebcaba0885f3a0da3d5b361069fcacd..36622f7b31f826b763688caddc1d214cc617df95 100644
--- a/sandbox/linux/bpf_dsl/bpf_dsl.h
+++ b/sandbox/linux/bpf_dsl/bpf_dsl.h
@@ -112,6 +112,7 @@ class SANDBOX_EXPORT SandboxBPFDSLPolicy : public SandboxBPFPolicy {
   virtual ErrorCode EvaluateSyscall(SandboxBPF* sb,
                                     int sysno) const OVERRIDE FINAL;
   virtual ErrorCode InvalidSyscall(SandboxBPF* sb) const OVERRIDE FINAL;
+  virtual bool HasUnsafeTraps() const OVERRIDE FINAL;
 
   // Helper method so policies can just write Trap(func, aux).
   static ResultExpr Trap(Trap::TrapFnc trap_func, const void* aux);
@@ -325,6 +326,7 @@ class SANDBOX_EXPORT ResultExprImpl : public base::RefCounted<ResultExprImpl> {
  public:
   ResultExprImpl() {}
   virtual ErrorCode Compile(SandboxBPF* sb) const = 0;
+  virtual bool HasUnsafeTraps() const;
 
  protected:
   virtual ~ResultExprImpl() {}