Change kUpdateThumbnailTime to be a TimeDelta.

Fixes a future warning with -Wshorten-64-to-32.

../../components/history/core/common/thumbnail_score_unittest.cc(86,33):  warning: implicit conversion loses integer precision: 'const int64_t' (aka 'const long long') to 'int' [-Wshorten-64-to-32]
      base::TimeDelta::FromDays(ThumbnailScore::kUpdateThumbnailTimeDays);
      ~~~~                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Also, remove an unused definition and some minor cleanup.

BUG=588506

Change-Id: I447c758454d0868cf1d023772c05464bc6e40262
Reviewed-on: https://chromium-review.googlesource.com/1195656Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Will Harris <wfh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587350}

components/history/core/common/thumbnail_score.cc

@@ -10,9 +10,13 @@
 using base::Time;
 using base::TimeDelta;
 
-const int64_t ThumbnailScore::kUpdateThumbnailTimeDays = 1;
+// static
 const double ThumbnailScore::kThumbnailMaximumBoringness = 0.94;
+// static
+const TimeDelta ThumbnailScore::kUpdateThumbnailTime = TimeDelta::FromDays(1);
+// static
 const double ThumbnailScore::kThumbnailDegradePerHour = 0.01;
+// static
 const double ThumbnailScore::kTooWideAspectRatio = 2.0;
 
 // Calculates a numeric score from traits about where a snapshot was
@@ -130,8 +134,8 @@ bool ShouldReplaceThumbnailWith(const ThumbnailScore& current,
 
 bool ThumbnailScore::ShouldConsiderUpdating() {
   const TimeDelta time_elapsed = Time::Now() - time_at_snapshot;
-  if (time_elapsed < TimeDelta::FromDays(kUpdateThumbnailTimeDays) &&
-      good_clipping && at_top && load_completed) {
+  if (time_elapsed < kUpdateThumbnailTime && good_clipping && at_top &&
+      load_completed) {
     // The current thumbnail is new and has good properties.
     return false;
   }

components/history/core/common/thumbnail_score.h

@@ -84,14 +84,10 @@ struct ThumbnailScore {
   // How bad a thumbnail needs to be before we completely ignore it.
   static const double kThumbnailMaximumBoringness;
 
-  // We consider a thumbnail interesting enough if the boring score is
-  // lower than this.
-  static const double kThumbnailInterestingEnoughBoringness;
-
   // Time before we take a worse thumbnail (subject to
   // kThumbnailMaximumBoringness) over what's currently in the database
   // for freshness.
-  static const int64_t kUpdateThumbnailTimeDays;
+  static const base::TimeDelta kUpdateThumbnailTime;
 
   // Penalty of how much more boring a thumbnail should be per hour.
   static const double kThumbnailDegradePerHour;

components/history/core/common/thumbnail_score_unittest.cc

@@ -82,7 +82,6 @@ TEST(ThumbnailScoreTest, ShouldConsiderUpdating) {
   EXPECT_FALSE(score.ShouldConsiderUpdating());
 
   // Make it old. Then, it's no longer new enough.
-  score.time_at_snapshot -=
-      base::TimeDelta::FromDays(ThumbnailScore::kUpdateThumbnailTimeDays);
+  score.time_at_snapshot -= ThumbnailScore::kUpdateThumbnailTime;
   EXPECT_TRUE(score.ShouldConsiderUpdating());
 }