BackoffEntry: Add the option to always use a delay.

net/base/backoff_entry.h

Index: net/base/backoff_entry.h
===================================================================
--- net/base/backoff_entry.h	(revision 133709)
+++ net/base/backoff_entry.h	(working copy)
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef NET_BASE_BACKOFF_ITEM_H_
-#define NET_BASE_BACKOFF_ITEM_H_
+#ifndef NET_BASE_BACKOFF_ENTRY_H_
+#define NET_BASE_BACKOFF_ENTRY_H_
 #pragma once
 
 #include "base/threading/non_thread_safe.h"
@@ -17,8 +17,7 @@
 //
 // This utility class knows nothing about network specifics; it is
 // intended for reuse in various networking scenarios.
-class NET_EXPORT_PRIVATE BackoffEntry
-    : NON_EXPORTED_BASE(public base::NonThreadSafe) {
+class NET_EXPORT BackoffEntry : NON_EXPORTED_BASE(public base::NonThreadSafe) {
  public:
   // The set of parameters that define a back-off policy.
   struct Policy {
@@ -26,8 +25,11 @@
     // exponential back-off rules.
     int num_errors_to_ignore;
 
-    // Initial delay for exponential back-off.
-    int initial_backoff_ms;
+    // Initial delay.  The interpretation of this value depends on
+    // always_use_initial_delay.  It's either how long we wait between
+    // requests before backoff starts, or how much we delay the first request
+    // after backoff starts.
+    int initial_delay_ms;
 
     // Factor by which the waiting time will be multiplied.
     double multiply_factor;
@@ -43,6 +45,15 @@
     // Time to keep an entry from being discarded even when it
     // has no significant state, -1 to never discard.
     int64 entry_lifetime_ms;
+
+    // If true, we always use a delay of initial_delay_ms, even before
+    // we've seen num_errors_to_ignore errors.  Otherwise, initial_delay_ms
+    // 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
@@ -62,13 +73,16 @@
   // state) will no longer reject requests.
   base::TimeTicks GetReleaseTime() const;
 
+  // Returns the time until a request can be sent.
+  base::TimeDelta GetTimeUntilRelease() const;
+
   // Causes this object reject requests until the specified absolute time.
   // This can be used to e.g. implement support for a Retry-After header.
   void SetCustomReleaseTime(const base::TimeTicks& release_time);
 
   // Returns true if this object has no significant state (i.e. you could
   // just as well start with a fresh BackoffEntry object), and hasn't
-  // had for Policy::entry_lifetime_ms_.
+  // had for Policy::entry_lifetime_ms.
   bool CanDiscard() const;
 
   // Resets this entry to a fresh (as if just constructed) state.
@@ -89,7 +103,7 @@
   // allowed to start sending requests again.
   base::TimeTicks exponential_backoff_release_time_;
 
-  // Counts request errors; reset on success.
+  // Counts request errors; decremented on success.
   int failure_count_;
 
   const Policy* const policy_;
@@ -99,4 +113,4 @@
 
 }  // namespace net
 
-#endif  // NET_BASE_BACKOFF_ITEM_H_
+#endif  // NET_BASE_BACKOFF_ENTRY_H_