[cookies] add a UMA for isPersistent bit

Let's track the distribution here.

Bug: 40285083
Change-Id: I2308419c3394d0271ba7a2c28f90af6299f39519
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6353699
Auto-Submit: Ari Chivukula <arichiv@chromium.org>
Reviewed-by: Steven Bingler <bingler@chromium.org>
Commit-Queue: Ari Chivukula <arichiv@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1432442}

net/cookies/cookie_monster.cc

@@ -443,11 +443,12 @@ CountCookiesAndGenerateListsForPossibleDeletionPartitionedCookies(
   return could_be_deleted;
 }
 
-// Records minutes until the expiration date of a cookie to the appropriate
-// histogram. Only histograms cookies that have an expiration date (i.e. are
-// persistent).
-void HistogramExpirationDuration(const CanonicalCookie& cookie,
+// Records whether the cookie being set is persistent. If so, this also records
+// minutes until the expiration date of a cookie to the appropriate histogram.
+void RecordPersistanceHistograms(const CanonicalCookie& cookie,
                                  base::Time creation_time) {
+  base::UmaHistogramBoolean("Cookie.IsPersistentWhenSet.Subsampled",
+                            cookie.IsPersistent());
   if (!cookie.IsPersistent())
     return;
 
@@ -1798,7 +1799,7 @@ void CookieMonster::SetCanonicalCookie(
     // was to delete the cookie which we've already done.
     if (!already_expired) {
       if (collect_metrics) {
-        HistogramExpirationDuration(*cc, creation_date);
+        RecordPersistanceHistograms(*cc, creation_date);
 
         base::UmaHistogramBoolean("Cookie.DomainSet.Subsampled",
                                   cc->IsDomainCookie());
@@ -1874,7 +1875,7 @@ void CookieMonster::SetAllCookies(CookieList list,
       continue;
 
     if (metrics_subsampler_.ShouldSample(kHistogramSampleProbability)) {
-      HistogramExpirationDuration(cookie, creation_time);
+      RecordPersistanceHistograms(cookie, creation_time);
     }
 
     CookieAccessResult access_result;

net/cookies/cookie_monster_unittest.cc

@@ -4704,9 +4704,15 @@ TEST_F(CookieMonsterTest, HistogramCheck) {
   base::HistogramBase* expired_histogram = base::Histogram::FactoryGet(
       "Cookie.ExpirationDurationMinutesSecure.Subsampled2", 1, 400 * 24 * 60,
       100, base::Histogram::kUmaTargetedHistogramFlag);
+  base::HistogramBase* persistance_histogram =
+      base::BooleanHistogram::FactoryGet(
+          "Cookie.IsPersistentWhenSet.Subsampled",
+          base::HistogramBase::kUmaTargetedHistogramFlag);
 
-  std::unique_ptr<base::HistogramSamples> samples1(
+  std::unique_ptr<base::HistogramSamples> expired_samples1(
       expired_histogram->SnapshotSamples());
+  std::unique_ptr<base::HistogramSamples> persistance_samples1(
+      persistance_histogram->SnapshotSamples());
   auto cookie = CanonicalCookie::CreateUnsafeCookieForTesting(
       "a", "b", "a.url", "/", base::Time(),
       base::Time::Now() + base::Minutes(59), base::Time(), base::Time(),
@@ -4717,16 +4723,26 @@ TEST_F(CookieMonsterTest, HistogramCheck) {
   ASSERT_TRUE(SetCanonicalCookie(cm.get(), std::move(cookie), source_url,
                                  /*modify_httponly=*/true));
 
-  std::unique_ptr<base::HistogramSamples> samples2(
+  std::unique_ptr<base::HistogramSamples> expired_samples2(
       expired_histogram->SnapshotSamples());
-  EXPECT_EQ(samples1->TotalCount() + 1, samples2->TotalCount());
+  std::unique_ptr<base::HistogramSamples> persistance_samples2(
+      persistance_histogram->SnapshotSamples());
+  EXPECT_EQ(expired_samples1->TotalCount() + 1, expired_samples2->TotalCount());
+  EXPECT_EQ(persistance_samples1->TotalCount() + 1,
+            persistance_samples2->TotalCount());
+  EXPECT_EQ(1, persistance_samples2->sum());
 
   // kValidCookieLine creates a session cookie.
   ASSERT_TRUE(SetCookie(cm.get(), http_www_foo_.url(), kValidCookieLine));
 
-  std::unique_ptr<base::HistogramSamples> samples3(
+  std::unique_ptr<base::HistogramSamples> expired_samples3(
       expired_histogram->SnapshotSamples());
-  EXPECT_EQ(samples2->TotalCount(), samples3->TotalCount());
+  std::unique_ptr<base::HistogramSamples> persistance_samples3(
+      persistance_histogram->SnapshotSamples());
+  EXPECT_EQ(expired_samples2->TotalCount(), expired_samples3->TotalCount());
+  EXPECT_EQ(persistance_samples2->TotalCount() + 1,
+            persistance_samples3->TotalCount());
+  EXPECT_EQ(1, persistance_samples3->sum());
 }
 
 TEST_F(CookieMonsterTest, InvalidExpiryTime) {

tools/metrics/histograms/metadata/cookie/histograms.xml

@@ -604,6 +604,20 @@ chromium-metrics-reviews@google.com.
   </summary>
 </histogram>
 
+<histogram name="Cookie.IsPersistentWhenSet.Subsampled" enum="Boolean"
+    expires_after="2025-10-31">
+  <owner>arichiv@chromium.org</owner>
+  <owner>kaustubhag@chromium.org</owner>
+  <owner>bingler@chromium.org</owner>
+  <summary>
+    Whether a cookie set via CookieMonster::SetCanonicalCookie or
+    CookieMonster::SetAllCookies is persistent (true) or session (false).
+
+    Subsampled to 1/1000. See kHistogramSampleProbability in
+    net/cookies/cookie_constants.h for details.
+  </summary>
+</histogram>
+
 <histogram name="Cookie.LoadProblem" enum="CookieLoadProblem"
     expires_after="2025-08-17">
   <owner>morlovich@chromium.org</owner>