[NTP Snippets] Add metric for fetch error cases

components/ntp_snippets/ntp_snippets_fetcher_unittest.cc

Index: components/ntp_snippets/ntp_snippets_fetcher_unittest.cc
diff --git a/components/ntp_snippets/ntp_snippets_fetcher_unittest.cc b/components/ntp_snippets/ntp_snippets_fetcher_unittest.cc
index 47cc5d4546e385e83fb856527114dd4aafa7d0b1..4f58b17c2eedf5e1fc365e1a2ef6f7f5f441b04c 100644
--- a/components/ntp_snippets/ntp_snippets_fetcher_unittest.cc
+++ b/components/ntp_snippets/ntp_snippets_fetcher_unittest.cc
@@ -6,6 +6,7 @@
 
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
+#include "base/test/histogram_tester.h"
 #include "base/thread_task_runner_handle.h"
 #include "net/url_request/test_url_fetcher_factory.h"
 #include "net/url_request/url_request_test_util.h"
@@ -15,6 +16,8 @@
 namespace ntp_snippets {
 namespace {
 
+using testing::ElementsAre;
+using testing::IsEmpty;
 using testing::IsNull;
 using testing::NotNull;
 
@@ -49,6 +52,8 @@ class NTPSnippetsFetcherTest : public testing::Test {
 
   MockSnippetsAvailableCallback& mock_callback() { return mock_callback_; }
 
+  base::HistogramTester& histogram_tester() { return histogram_tester_; }
+
  private:
   // Instantiation of factory automatically sets itself as URLFetcher's factory.
   net::FakeURLFetcherFactory fake_url_fetcher_factory_;
@@ -59,6 +64,7 @@ class NTPSnippetsFetcherTest : public testing::Test {
   std::unique_ptr<
       NTPSnippetsFetcher::SnippetsAvailableCallbackList::Subscription>
       snippets_fetcher_subscription_;
+  base::HistogramTester histogram_tester_;
 
   DISALLOW_COPY_AND_ASSIGN(NTPSnippetsFetcherTest);
 };
@@ -66,6 +72,12 @@ class NTPSnippetsFetcherTest : public testing::Test {
 TEST_F(NTPSnippetsFetcherTest, ShouldNotFetchOnCreation) {
   // The lack of registered baked in responses would cause any fetch to fail.
   base::RunLoop().RunUntilIdle();
+  EXPECT_THAT(
+      histogram_tester().GetAllSamples("NewTabPage.Snippets.FetchResponseCode"),
+      IsEmpty());
+  EXPECT_THAT(histogram_tester().GetAllSamples(
+                  "NewTabPage.Snippets.FailedRequestErrorCode"),
+              IsEmpty());
 }
 
 TEST_F(NTPSnippetsFetcherTest, ShouldFetchSuccessfully) {
@@ -79,6 +91,12 @@ TEST_F(NTPSnippetsFetcherTest, ShouldFetchSuccessfully) {
   snippets_fetcher().FetchSnippets(/*hosts=*/std::set<std::string>(),
                                    /*count=*/1);
   base::RunLoop().RunUntilIdle();
+  EXPECT_THAT(
+      histogram_tester().GetAllSamples("NewTabPage.Snippets.FetchResponseCode"),
+      ElementsAre(base::Bucket(/*min=*/200, /*count=*/1)));
+  EXPECT_THAT(histogram_tester().GetAllSamples(
+                  "NewTabPage.Snippets.FailedRequestErrorCode"),
+              IsEmpty());
 }
 
 TEST_F(NTPSnippetsFetcherTest, ShouldReportUrlStatusError) {
@@ -93,6 +111,12 @@ TEST_F(NTPSnippetsFetcherTest, ShouldReportUrlStatusError) {
   snippets_fetcher().FetchSnippets(/*hosts=*/std::set<std::string>(),
                                    /*count=*/1);
   base::RunLoop().RunUntilIdle();
+  EXPECT_THAT(
+      histogram_tester().GetAllSamples("NewTabPage.Snippets.FetchResponseCode"),
+      IsEmpty());
+  EXPECT_THAT(histogram_tester().GetAllSamples(
+                  "NewTabPage.Snippets.FailedRequestErrorCode"),
+              ElementsAre(base::Bucket(/*min=*/2, /*count=*/1)));
 }
 
 TEST_F(NTPSnippetsFetcherTest, ShouldReportHttpError) {
@@ -106,6 +130,12 @@ TEST_F(NTPSnippetsFetcherTest, ShouldReportHttpError) {
   snippets_fetcher().FetchSnippets(/*hosts=*/std::set<std::string>(),
                                    /*count=*/1);
   base::RunLoop().RunUntilIdle();
+  EXPECT_THAT(
+      histogram_tester().GetAllSamples("NewTabPage.Snippets.FetchResponseCode"),
+      ElementsAre(base::Bucket(/*min=*/404, /*count=*/1)));
+  EXPECT_THAT(histogram_tester().GetAllSamples(
+                  "NewTabPage.Snippets.FailedRequestErrorCode"),
+              IsEmpty());
 }
 
 TEST_F(NTPSnippetsFetcherTest, ShouldCancelOngoingFetch) {
@@ -123,6 +153,12 @@ TEST_F(NTPSnippetsFetcherTest, ShouldCancelOngoingFetch) {
   snippets_fetcher().FetchSnippets(/*hosts=*/std::set<std::string>(),
                                    /*count=*/1);
   base::RunLoop().RunUntilIdle();
+  EXPECT_THAT(
+      histogram_tester().GetAllSamples("NewTabPage.Snippets.FetchResponseCode"),
+      ElementsAre(base::Bucket(/*min=*/200, /*count=*/1)));
+  EXPECT_THAT(histogram_tester().GetAllSamples(
+                  "NewTabPage.Snippets.FailedRequestErrorCode"),
+              IsEmpty());
 }
 
 }  // namespace