Refactor net::BackoffEntry to not require subclassing

net/base/backoff_entry.h

 // Copyright (c) 2012 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 NET_BASE_BACKOFF_ENTRY_H_
 #define NET_BASE_BACKOFF_ENTRY_H_
 
 #include "base/threading/non_thread_safe.h"
 #include "base/time/time.h"
 #include "net/base/net_export.h"
 
+namespace base {
+class TickClock;
+}
+
 namespace net {
 
 // Provides the core logic needed for randomized exponential back-off
 // on requests to a given resource, given a back-off policy.
 //
 // This utility class knows nothing about network specifics; it is
 // intended for reuse in various networking scenarios.
 class NET_EXPORT BackoffEntry : NON_EXPORTED_BASE(public base::NonThreadSafe) {
  public:
   // The set of parameters that define a back-off policy.
@@ skipping 28 matching lines @@
     // is the first delay once we start exponential backoff.
     //
     // So if we're ignoring 1 error, we'll see (N, N, Nm, Nm^2, ...) if true,
     // and (0, 0, N, Nm, ...) when false, where N is initial_backoff_ms and
     // m is multiply_factor, assuming we've already seen one success.
     bool always_use_initial_delay;
   };
 
   // Lifetime of policy must enclose lifetime of BackoffEntry. The
   // pointer must be valid but is not dereferenced during construction.
-  explicit BackoffEntry(const Policy* const policy);
+  explicit BackoffEntry(const Policy* policy);
+  // Lifetime of policy and clock must enclose lifetime of BackoffEntry.
+  // |policy| pointer must be valid but isn't dereferenced during construction.
+  // |clock| pointer may be null.
+  BackoffEntry(const Policy* policy, base::TickClock* clock);
   virtual ~BackoffEntry();
 
   // Inform this item that a request for the network resource it is
   // tracking was made, and whether it failed or succeeded.
   void InformOfRequest(bool succeeded);
 
   // Returns true if a request for the resource this item tracks should
   // be rejected at the present time due to exponential back-off policy.
   bool ShouldRejectRequest() const;
 
@@ skipping 12 matching lines @@
   // just as well start with a fresh BackoffEntry object), and hasn't
   // had for Policy::entry_lifetime_ms.
   bool CanDiscard() const;
 
   // Resets this entry to a fresh (as if just constructed) state.
   void Reset();
 
   // Returns the failure count for this entry.
   int failure_count() const { return failure_count_; }
 
- protected:
-  // Equivalent to TimeTicks::Now(), virtual so unit tests can override.
-  virtual base::TimeTicks ImplGetTimeNow() const;
-
  private:
   // Calculates when requests should again be allowed through.
   base::TimeTicks CalculateReleaseTime() const;
 
+  // Equivalent to TimeTicks::Now(), using clock_ if provided.
+  base::TimeTicks GetTimeTicksNow() const;
+
   // Timestamp calculated by the exponential back-off algorithm at which we are
   // allowed to start sending requests again.
   base::TimeTicks exponential_backoff_release_time_;
 
   // Counts request errors; decremented on success.
   int failure_count_;
 
-  const Policy* const policy_;
+  const Policy* const policy_;  // Not owned.
+
+  base::TickClock* const clock_;  // Not owned.
 
   DISALLOW_COPY_AND_ASSIGN(BackoffEntry);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_BACKOFF_ENTRY_H_