[LanguageModel] Clear the model when clearing full history

components/translate/core/browser/language_model_unittest.cc

Index: components/translate/core/browser/language_model_unittest.cc
diff --git a/components/translate/core/browser/language_model_unittest.cc b/components/translate/core/browser/language_model_unittest.cc
index df8b6bad29de2f8b510d0115d36a8e08fec27348..cfa901ba15e552e6ab299f37149650b830f5ecdc 100644
--- a/components/translate/core/browser/language_model_unittest.cc
+++ b/components/translate/core/browser/language_model_unittest.cc
@@ -11,6 +11,7 @@
 using testing::ElementsAre;
 using testing::FloatEq;
 using testing::Gt;
+using testing::SizeIs;
 
 namespace {
 
@@ -105,4 +106,42 @@ TEST(LanguageModelTest, RareLanguageDiscarded) {
               ElementsAre(LanguageModel::LanguageInfo{kLang1, 1}));
 }
 
+TEST(LanguageModelTest, ShouldClearHistoryIfAllTimes) {
+  TestingPrefServiceSimple prefs;
+  LanguageModel::RegisterProfilePrefs(prefs.registry());
+  LanguageModel model(&prefs);
+
+  for (int i = 0; i < 100; i++) {
+    model.OnPageVisited(kLang1);
+  }
+
+  EXPECT_THAT(model.GetTopLanguages(), SizeIs(1));
+  EXPECT_THAT(model.GetLanguageFrequency(kLang1), FloatEq(1.0));
+
+  model.ClearHistory(base::Time(), base::Time::Max());
+
+  EXPECT_THAT(model.GetTopLanguages(), SizeIs(0));
+  EXPECT_THAT(model.GetLanguageFrequency(kLang1), FloatEq(0.0));
+}
+
+TEST(LanguageModelTest, ShouldNotClearHistoryIfNotAllTimes) {
+  TestingPrefServiceSimple prefs;
+  LanguageModel::RegisterProfilePrefs(prefs.registry());
+  LanguageModel model(&prefs);
+
+  for (int i = 0; i < 100; i++) {
+    model.OnPageVisited(kLang1);
+  }
+
+  EXPECT_THAT(model.GetTopLanguages(), SizeIs(1));
+  EXPECT_THAT(model.GetLanguageFrequency(kLang1), FloatEq(1.0));
+
+  // Clearing only the last hour of the history has no effect.
+  model.ClearHistory(base::Time::Now() - base::TimeDelta::FromHours(1),

[groby-ooo-7-16, 2017/01/25 16:12:45]

Would you mind making this more than an hour? Because otherwise I'll always
worry what happens at DST switch :) (I know it won't break. Just the "time is
evil" part of my brain will be triggered ;)

[jkrcal, 2017/01/26 15:46:22]

Done. Thanks for pointing out! 

Actually, "1 hour" is spread all around the browsing_data_remover unit tests.
Maybe something to consider changing, Martin? ;) 

[msramek, 2017/01/26 16:00:48]

I'm pretty sure base::Time() is UTC. So base::TimeDelta::FromHours(1) is always
an hour ago. I would be more worried about Chrome travelling at lightspeed or
falling into a black hole than DST shifts :)

Even if it wasn't, we have to delete data using the same units with which they
were written, which is again usually base::Time().

Note that we do take DST shifts into account in places like the history page,
which cuts the entries into blocks from local midnight to local midnight - that
might be 23 or 25 hours sometimes.

+                     base::Time::Max());
+
+  EXPECT_THAT(model.GetTopLanguages(), SizeIs(1));
+  EXPECT_THAT(model.GetLanguageFrequency(kLang1), FloatEq(1.0));
+}
+
 }  // namespace translate