PlzNavigate: Add metrics to understand bf navigations PLT regression

content/browser/loader/resource_dispatcher_host_impl.cc

Index: content/browser/loader/resource_dispatcher_host_impl.cc
diff --git a/content/browser/loader/resource_dispatcher_host_impl.cc b/content/browser/loader/resource_dispatcher_host_impl.cc
index 300a222f6acc42fbebe46bb6efe44d9f17e486ca..1807e9174956d92c5df6ba65a107ef1566fca6ed 100644
--- a/content/browser/loader/resource_dispatcher_host_impl.cc
+++ b/content/browser/loader/resource_dispatcher_host_impl.cc
@@ -272,6 +272,45 @@ void HandleSyncLoadResult(base::WeakPtr<ResourceMessageFilter> filter,
   filter->Send(sync_result.release());
 }
 
+// Used to log the cache flags for back-forward navigation requests.

[Ilya Sherman, 2017/06/13 21:38:00]

Please document that this is used to back an UMA histogram, and should therefore
be treated as append-only.

[clamy, 2017/06/14 13:26:50]

Done.

+// TODO(clamy): Remove this once we know the reason behind PlzNavigate's
+// regression on PLT for back forward navigations.
+enum HistogramCacheFlag {
+  HISTOGRAM_VALIDATE_CACHE,
+  HISTOGRAM_BYPASS_CACHE,
+  HISTOGRAM_SKIP_CACHE_VALIDATION,
+  HISTOGRAM_ONLY_FROM_CACHE,
+  HISTOGRAM_DISABLE_CACHE,
+  HISTOGRAM_CACHE_FLAG_MAX = HISTOGRAM_DISABLE_CACHE,
+};
+
+void LogBackForwardNavigationFlagsHistogram(int load_flags) {
+  if (load_flags & net::LOAD_VALIDATE_CACHE) {
+    UMA_HISTOGRAM_ENUMERATION("Navigation.BackForward.CacheFlags",
+                              HISTOGRAM_VALIDATE_CACHE,
+                              HISTOGRAM_CACHE_FLAG_MAX);

[Ilya Sherman, 2017/06/13 21:38:00]

nit: Please create a small wrapper function, that could be called like
RecordCacheFlags(HISTOGRAM_VALIDATE_CACHE).  The UMA_HISTOGRAM_* macros expand
to a fair bit of code, so it's nice to help the compiler not duplicate that (and
also help avoid typos sneaking in to just some of the code paths).

[clamy, 2017/06/14 13:26:50]

Done.

+  }
+  if (load_flags & net::LOAD_BYPASS_CACHE) {
+    UMA_HISTOGRAM_ENUMERATION("Navigation.BackForward.CacheFlags",
+                              HISTOGRAM_BYPASS_CACHE, HISTOGRAM_CACHE_FLAG_MAX);
+  }
+  if (load_flags & net::LOAD_SKIP_CACHE_VALIDATION) {
+    UMA_HISTOGRAM_ENUMERATION("Navigation.BackForward.CacheFlags",
+                              HISTOGRAM_SKIP_CACHE_VALIDATION,
+                              HISTOGRAM_CACHE_FLAG_MAX);
+  }
+  if (load_flags & net::LOAD_ONLY_FROM_CACHE) {
+    UMA_HISTOGRAM_ENUMERATION("Navigation.BackForward.CacheFlags",
+                              HISTOGRAM_ONLY_FROM_CACHE,
+                              HISTOGRAM_CACHE_FLAG_MAX);
+  }
+  if (load_flags & net::LOAD_VALIDATE_CACHE) {
+    UMA_HISTOGRAM_ENUMERATION("Navigation.BackForward.CacheFlags",
+                              HISTOGRAM_VALIDATE_CACHE,
+                              HISTOGRAM_CACHE_FLAG_MAX);
+  }
+}
+
 }  // namespace
 
 ResourceDispatcherHostImpl::LoadInfo::LoadInfo() {}
@@ -2200,6 +2239,14 @@ void ResourceDispatcherHostImpl::BeginRequestInternal(
   ResourceRequestInfoImpl* info =
       ResourceRequestInfoImpl::ForRequest(request.get());
 
+  // Log metrics for back-forward navigations.
+  // TODO(clamy): Remove this once we understand the reason behind the
+  // back-forward PLT regression with PlzNavigate
+  if ((info->GetPageTransition() & ui::PAGE_TRANSITION_FORWARD_BACK) &&
+      IsResourceTypeFrame(info->GetResourceType())) {

[nasko, 2017/06/13 23:50:08]

Since we care only about main resources, shouldn't this code be added only to
ResourceDispatcherHostImpl::BeginNavigationRequest? Or is the goal to capture
both PlzNavigate and regular navigation cases?

[clamy, 2017/06/14 13:26:50]

Yes the goal is to compare between PlzNavigate and non PlzNavigate for all
histograms.

+    LogBackForwardNavigationFlagsHistogram(request->load_flags());
+  }
+
   if ((TimeTicks::Now() - last_user_gesture_time_) <
       TimeDelta::FromMilliseconds(kUserGestureWindowMs)) {
     request->SetLoadFlags(request->load_flags() | net::LOAD_MAYBE_USER_GESTURE);