[NoStatePrefetch] Add UMA histogram to count prefetch requests

chrome/browser/prerender/prerender_histograms.cc

Index: chrome/browser/prerender/prerender_histograms.cc
diff --git a/chrome/browser/prerender/prerender_histograms.cc b/chrome/browser/prerender/prerender_histograms.cc
index 3e4b4bfa1915016af5bb4cf47d24037264b2f2f0..7afe01dccfb5830c4e3465ceee1aad9e842c6b36 100644
--- a/chrome/browser/prerender/prerender_histograms.cc
+++ b/chrome/browser/prerender/prerender_histograms.cc
@@ -7,18 +7,29 @@
 #include <string>
 
 #include "base/format_macros.h"
+#include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "base/strings/stringprintf.h"
-#include "chrome/browser/predictors/autocomplete_action_predictor.h"
 #include "chrome/browser/prerender/prerender_manager.h"
 #include "chrome/browser/prerender/prerender_util.h"
 
-using predictors::AutocompleteActionPredictor;
-
 namespace prerender {
 
 namespace {
 
+// This enum is used to define the buckets for the
+// "Prerender.NoStatePrefetchResourceCount" histogram family.
+// Hence, existing enumerated constants should never be deleted or reordered,
+// and new constants should only be appended at the end of the enumeration.
+enum NoStatePrefetchResourceType {
+  MAIN_RESOURCE_CACHEABLE = 0,
+  MAIN_RESOURCE_NO_STORE = 1,
+  SUB_RESOURCE_CACHEABLE = 2,
+  SUB_RESOURCE_NO_STORE = 3,
+
+  NO_STATE_PREFETCH_RESOURCE_TYPE_COUNT  // Must be the last.
+};
+
 // Time window for which we will record windowed PLTs from the last observed
 // link rel=prefetch tag. This is not intended to be the same as the prerender
 // ttl, it's just intended to be a window during which a prerender has likely
@@ -383,6 +394,28 @@ void PrerenderHistograms::RecordNetworkBytes(Origin origin,
   }
 }
 
+void PrerenderHistograms::RecordResourcePrefetch(Origin origin,
+                                                 bool is_main_resource,
+                                                 bool is_no_store) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  NoStatePrefetchResourceType type =
+      is_main_resource
+          ? (is_no_store ? MAIN_RESOURCE_NO_STORE : MAIN_RESOURCE_CACHEABLE)
+          : (is_no_store ? SUB_RESOURCE_NO_STORE : SUB_RESOURCE_CACHEABLE);
+  DCHECK_LT(type, NO_STATE_PREFETCH_RESOURCE_TYPE_COUNT);
+
+  std::string histogram_name =
+      GetHistogramName(origin, IsOriginWash(), "NoStatePrefetchResourceCount");

[pasko, 2016/08/30 15:11:19]

nit: I think "Count" is implied in histograms, BlahResourceType might sound
slightly more informative, up to you

+
+  // Unrolls UMA_HISTOGRAM_ENUMERATION, required to support dynamic histogram
+  // name.
+  base::HistogramBase* histogram_pointer = base::LinearHistogram::FactoryGet(
+      histogram_name, 1, NO_STATE_PREFETCH_RESOURCE_TYPE_COUNT,
+      NO_STATE_PREFETCH_RESOURCE_TYPE_COUNT + 1,
+      base::HistogramBase::kUmaTargetedHistogramFlag);
+  histogram_pointer->Add(type);
+}
+
 bool PrerenderHistograms::IsOriginWash() const {
   if (!WithinWindow())
     return false;