android: Fix another Wrange-loop-analysis warning.

Bug: 1039697
Change-Id: I18ede84f1632aedb29a0a34730e884fafc9cc4f4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2071508
Commit-Queue: Nico Weber <thakis@chromium.org>
Commit-Queue: Kentaro Hara <haraken@chromium.org>
Auto-Submit: Nico Weber <thakis@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#744171}

chrome/browser/offline_pages/offline_page_request_handler_unittest.cc

@@ -661,7 +661,7 @@ void OfflinePageRequestHandlerTest::ExpectOfflinePageSizeTotalSuffixCount(
   base::HistogramTester::CountsMap all_offline_counts =
       histogram_tester_->GetTotalCountsForPrefix(
           kPageSizeAccessOfflineHistogramBase);
-  for (const std::pair<std::string, base::HistogramBase::Count>&
+  for (const std::pair<const std::string, base::HistogramBase::Count>&
            namespace_and_count : all_offline_counts) {
     total_offline_count += namespace_and_count.second;
   }
@@ -684,7 +684,7 @@ void OfflinePageRequestHandlerTest::ExpectOnlinePageSizeTotalSuffixCount(
   base::HistogramTester::CountsMap all_online_counts =
       histogram_tester_->GetTotalCountsForPrefix(
           kPageSizeAccessOnlineHistogramBase);
-  for (const std::pair<std::string, base::HistogramBase::Count>&
+  for (const std::pair<const std::string, base::HistogramBase::Count>&
            namespace_and_count : all_online_counts) {
     online_count += namespace_and_count.second;
   }