Produces local history zero-prefix suggestions for signed-in users

Otherwise signing in could make the user experience worse, if there aren't
enough remote suggestions, e.g., a user with local history but a fresh
Google account or server's failure to return remote suggestions.

Bug: 996516,1021244
Change-Id: I9cbfebadc5a7e7e1d6e204890d668cc8b9f59984
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1898299Reviewed-by: Tommy Li <tommycli@chromium.org>
Commit-Queue: Moe Ahmadi <mahmadi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712322}

components/omnibox/browser/local_history_zero_suggest_provider.cc

@@ -68,9 +68,9 @@ void LocalHistoryZeroSuggestProvider::Start(const AutocompleteInput& input,
   done_ = true;
   matches_.clear();
 
-  // Allow local history query suggestions only when the user is unauthenticated
-  // and is not in an off-the-record context.
-  if (client_->IsAuthenticated() || client_->IsOffTheRecord())
+  // Allow local history query suggestions only when the user is not in an
+  // off-the-record context.
+  if (client_->IsOffTheRecord())
     return;
 
   // Allow local history query suggestions only when the omnibox is empty and is

components/omnibox/browser/local_history_zero_suggest_provider_unittest.cc

@@ -253,6 +253,26 @@ TEST_F(LocalHistoryZeroSuggestProviderTest, Input) {
       "Omnibox.LocalHistoryZeroSuggest.AsyncDeleteTime", 0);
 }
 
+// Tests that suggestions are returned only user is not in an off-the-record
+// context, regardless of the user's authentication state.
+TEST_F(LocalHistoryZeroSuggestProviderTest, Incognito) {
+  LoadURLs({
+      {default_search_provider(), "hello world", "&foo=bar", 1},
+  });
+
+  EXPECT_CALL(*client_.get(), IsAuthenticated()).Times(0);
+  EXPECT_CALL(*client_.get(), IsOffTheRecord())
+      .Times(2)
+      .WillOnce(testing::Return(true))
+      .WillOnce(testing::Return(false));
+
+  StartProviderAndWaitUntilDone();
+  ExpectMatches({});
+
+  StartProviderAndWaitUntilDone();
+  ExpectMatches({{"hello world", 500}});
+}
+
 // Tests that suggestions are returned only if ZeroSuggestVariant is configured
 // to return local history suggestions in the NTP.
 TEST_F(LocalHistoryZeroSuggestProviderTest, ZeroSuggestVariant) {