Add a TimeUntilNextTry to reading list

ios/chrome/browser/reading_list/reading_list_entry_unittest.cc

 // Copyright 2016 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.
 
 #include "ios/chrome/browser/reading_list/reading_list_entry.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
 
 TEST(ReadingListEntry, CompareIgnoreTitle) {
   const ReadingListEntry e1(GURL("http://example.com"), "bar");
@@ skipping 32 matching lines @@
 
   EXPECT_EQ(ReadingListEntry::WAITING, e.DistilledState());
 
   e.SetDistilledState(ReadingListEntry::ERROR);
   EXPECT_EQ(ReadingListEntry::ERROR, e.DistilledState());
 
   const GURL distilled_url("http://distilled.example.com");
   e.SetDistilledURL(distilled_url);
   EXPECT_EQ(ReadingListEntry::PROCESSED, e.DistilledState());
 }
+
+// Tests the auto incrementation of the failed distillation counter.
+TEST(ReadingListEntry, FailedDistillationCounter) {
+  ReadingListEntry e(GURL("http://example.com"), "bar");
+
+  ASSERT_EQ(0, e.FailedDistillationCounter());
+
+  e.SetDistilledState(ReadingListEntry::ERROR);
+  EXPECT_EQ(1, e.FailedDistillationCounter());
+
+  e.SetDistilledState(ReadingListEntry::WILL_RETRY);

[noyau (Ping after 24h), 2016/09/16 14:25:13]

Is there any case where a transition from ERROR to WILL_RETRY is possible? Or
desirable? Should it be DCHECKed instead?

[gambard, 2016/09/19 09:08:09]

Potentially, if you launch two download before the first of the two has ended,
one finishing in ERROR and the other in WILL_RETRY. I don't know if it is
possible, but I don't want to prevent it.

+  EXPECT_EQ(1, e.FailedDistillationCounter());
+
+  e.SetDistilledState(ReadingListEntry::PROCESSING);
+  e.SetDistilledState(ReadingListEntry::WILL_RETRY);
+  EXPECT_EQ(2, e.FailedDistillationCounter());
+
+  e.SetDistilledState(ReadingListEntry::ERROR);
+  EXPECT_EQ(2, e.FailedDistillationCounter());
+}