BackForwardCache: Reset recorded metrics at navigations correctly

Before this CL, |BackForwardCacheMetrics::
browsing_instance_not_swapped_reason_| is not reset at navigation and
might be recorded in non-related navigations unexpectedly.

This CL fixes this by resetting it every navigation.

Bug: 1134847
Change-Id: Ib9e00f6937c5425c82cd2e40bdb47cb1fb740d38
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2501546Reviewed-by: Alexander Timin <altimin@chromium.org>
Commit-Queue: Hajime Hoshi <hajimehoshi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#822154}

content/browser/back_forward_cache_browsertest.cc

@@ -34,6 +34,7 @@
 #include "content/browser/renderer_host/frame_tree_node.h"
 #include "content/browser/renderer_host/page_lifecycle_state_manager.h"
 #include "content/browser/renderer_host/render_frame_host_impl.h"
+#include "content/browser/renderer_host/should_swap_browsing_instance.h"
 #include "content/browser/web_contents/file_chooser_impl.h"
 #include "content/browser/web_contents/web_contents_impl.h"
 #include "content/common/content_navigation_policy.h"
@@ -376,6 +377,30 @@ class BackForwardCacheBrowserTest : public ContentBrowserTest,
         << location.ToString();
   }
 
+  void ExpectBrowsingInstanceNotSwappedReason(ShouldSwapBrowsingInstance reason,
+                                              base::Location location) {
+    base::HistogramBase::Sample sample = base::HistogramBase::Sample(reason);
+    AddSampleToBuckets(&expected_browsing_instance_not_swapped_reasons_,
+                       sample);
+
+    EXPECT_THAT(histogram_tester_.GetAllSamples(
+                    "BackForwardCache.HistoryNavigationOutcome."
+                    "BrowsingInstanceNotSwappedReason"),
+                UnorderedElementsAreArray(
+                    expected_browsing_instance_not_swapped_reasons_))
+        << location.ToString();
+
+    if (!check_all_sites_)
+      return;
+
+    EXPECT_THAT(histogram_tester_.GetAllSamples(
+                    "BackForwardCache.AllSites.HistoryNavigationOutcome."
+                    "BrowsingInstanceNotSwappedReason"),
+                UnorderedElementsAreArray(
+                    expected_browsing_instance_not_swapped_reasons_))
+        << location.ToString();
+  }
+
   void ExpectEvictedAfterCommitted(
       std::vector<BackForwardCacheMetrics::EvictedAfterDocumentRestoredReason>
           reasons,
@@ -503,6 +528,7 @@ class BackForwardCacheBrowserTest : public ContentBrowserTest,
   std::vector<base::Bucket> expected_not_restored_;
   std::vector<base::Bucket> expected_blocklisted_features_;
   std::vector<base::Bucket> expected_disabled_reasons_;
+  std::vector<base::Bucket> expected_browsing_instance_not_swapped_reasons_;
   std::vector<base::Bucket> expected_eviction_after_committing_;
   std::unique_ptr<net::EmbeddedTestServer> https_server_;
   std::unordered_map<base::Feature,
@@ -2494,6 +2520,23 @@ IN_PROC_BROWSER_TEST_F(
         {blink::scheduler::WebSchedulerTrackedFeature::kWebRTC,
          blink::scheduler::WebSchedulerTrackedFeature::kKeyboardLock},
         FROM_HERE);
+    ExpectBrowsingInstanceNotSwappedReason(
+        ShouldSwapBrowsingInstance::kNo_NotNeededForBackForwardCache,
+        FROM_HERE);
+
+    web_contents()->GetController().GoForward();
+    EXPECT_TRUE(WaitForLoadStop(shell()->web_contents()));
+
+    ExpectBrowsingInstanceNotSwappedReason(
+        ShouldSwapBrowsingInstance::kNo_AlreadyHasMatchingBrowsingInstance,
+        FROM_HERE);
+
+    web_contents()->GetController().GoBack();
+    EXPECT_TRUE(WaitForLoadStop(shell()->web_contents()));
+
+    ExpectBrowsingInstanceNotSwappedReason(
+        ShouldSwapBrowsingInstance::kNo_AlreadyHasMatchingBrowsingInstance,
+        FROM_HERE);
   } else {
     ExpectNotRestored({BackForwardCacheMetrics::NotRestoredReason::
                            kRenderFrameHostReused_CrossSite},

content/browser/renderer_host/back_forward_cache_metrics.cc

@@ -123,6 +123,7 @@ void BackForwardCacheMetrics::DidCommitNavigation(
 
     not_restored_reasons_.reset();
     blocklisted_features_ = 0;
+    browsing_instance_not_swapped_reason_.reset();
     disabled_reasons_.clear();
     previous_navigation_is_served_from_bfcache_ =
         navigation->IsServedFromBackForwardCache();