Previews: Add UMA for Page End Reason on previews

Added in the Previews UKM observer which is most previews-generic PLM
observer we have.

See bug for more context.

Bug: 900466
Change-Id: I828728bf561e8253105b3b22a35b9e031b0266dd
Reviewed-on: https://chromium-review.googlesource.com/c/1313851
Commit-Queue: Robert Ogden <robertogden@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606135}

chrome/browser/page_load_metrics/observers/previews_ukm_observer.cc

@@ -4,6 +4,7 @@
 
 #include "chrome/browser/page_load_metrics/observers/previews_ukm_observer.h"
 
+#include "base/metrics/histogram_functions.h"
 #include "base/optional.h"
 #include "base/time/time.h"
 #include "chrome/browser/browser_process.h"
@@ -16,7 +17,6 @@
 #include "chrome/common/page_load_metrics/page_load_timing.h"
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_settings.h"
 #include "components/previews/content/previews_content_util.h"
-#include "components/previews/core/previews_experiments.h"
 #include "content/public/browser/navigation_handle.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/common/previews_state.h"
@@ -26,7 +26,8 @@
 
 namespace previews {
 
-PreviewsUKMObserver::PreviewsUKMObserver() {}
+PreviewsUKMObserver::PreviewsUKMObserver()
+    : committed_preview_(PreviewsType::NONE) {}
 
 PreviewsUKMObserver::~PreviewsUKMObserver() {}
 
@@ -47,6 +48,7 @@ PreviewsUKMObserver::OnCommit(content::NavigationHandle* navigation_handle,
   if (!previews_user_data)
     return STOP_OBSERVING;
 
+  committed_preview_ = previews_user_data->committed_previews_type();
   content::PreviewsState previews_state =
       previews_user_data->committed_previews_state();
   if (previews_state && previews::GetMainFramePreviewsType(previews_state) ==
@@ -106,6 +108,14 @@ void PreviewsUKMObserver::OnComplete(
 
 void PreviewsUKMObserver::RecordPreviewsTypes(
     const page_load_metrics::PageLoadExtraInfo& info) {
+  // Record the page end reason in UMA.
+  base::UmaHistogramExactLinear(
+      base::StringPrintf(
+          "Previews.PageEndReason.%s",
+          previews::GetStringNameForType(committed_preview_).c_str()),
+      info.page_end_reason,
+      page_load_metrics::PageEndReason::PAGE_END_REASON_COUNT);
+
   // Only record previews types when they are active.
   if (!server_lofi_seen_ && !client_lofi_seen_ && !lite_page_seen_ &&
       !noscript_seen_ && !resource_loading_hints_seen_ &&

chrome/browser/page_load_metrics/observers/previews_ukm_observer.h

@@ -8,6 +8,7 @@
 #include "base/macros.h"
 #include "base/sequence_checker.h"
 #include "chrome/browser/page_load_metrics/page_load_metrics_observer.h"
+#include "components/previews/core/previews_experiments.h"
 
 namespace content {
 class NavigationHandle;
@@ -49,6 +50,9 @@ class PreviewsUKMObserver : public page_load_metrics::PageLoadMetricsObserver {
  private:
   void RecordPreviewsTypes(const page_load_metrics::PageLoadExtraInfo& info);
 
+  // The preview type that was most recently committed.
+  PreviewsType committed_preview_;
+
   bool server_lofi_seen_ = false;
   bool client_lofi_seen_ = false;
   bool lite_page_seen_ = false;

components/previews/content/previews_user_data.cc

@@ -23,4 +23,9 @@ void PreviewsUserData::SetCommittedPreviewsType(
   committed_previews_type_ = previews_type;
 }
 
+void PreviewsUserData::SetCommittedPreviewsTypeForTesting(
+    previews::PreviewsType previews_type) {
+  committed_previews_type_ = previews_type;
+}
+
 }  // namespace previews

components/previews/content/previews_user_data.h

@@ -69,6 +69,8 @@ class PreviewsUserData {
   }
   // Sets the committed previews type. Should only be called once.
   void SetCommittedPreviewsType(previews::PreviewsType previews_type);
+  // Sets the committed previews type for testing. Can be called multiple times.
+  void SetCommittedPreviewsTypeForTesting(previews::PreviewsType previews_type);
 
   bool offline_preview_used() const { return offline_preview_used_; }
   // Whether an offline preview is being served.

tools/metrics/histograms/histograms.xml

@@ -83992,6 +83992,11 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="Previews.PageEndReason" enum="PageEndReason">
+  <owner>robertogden@chromium.org</owner>
+  <summary>Records why the page load ended on a given preview type.</summary>
+</histogram>
+
 <histogram name="Previews.ProcessHintsResult" enum="PreviewsProcessHintsResult">
   <owner>dougarnett@chromium.org</owner>
   <summary>
@@ -133905,6 +133910,7 @@ uploading your change for review.
   <suffix name="LitePage" label="Lite page previews"/>
   <suffix name="LitePageRedirect" label="Lite page redirection previews"/>
   <suffix name="LoFi" label="LoFi previews"/>
+  <suffix name="None" label="No preview was served"/>
   <suffix name="NoScript" label="NoScript previews"/>
   <suffix name="Offline" label="Offline previews"/>
   <suffix name="ResourceLoadingHints"
@@ -133914,6 +133920,7 @@ uploading your change for review.
   <affected-histogram name="Previews.OmniboxAction"/>
   <affected-histogram name="Previews.OptimizationFilterStatus"/>
   <affected-histogram name="Previews.OptOut.UserOptedOut"/>
+  <affected-histogram name="Previews.PageEndReason"/>
 </histogram_suffixes>
 
 <histogram_suffixes name="ProcessMemoryAllocator2" separator=".">