predictors: Add prefetching hit/miss histograms.

chrome/browser/predictors/resource_prefetch_predictor_browsertest.cc

Index: chrome/browser/predictors/resource_prefetch_predictor_browsertest.cc
diff --git a/chrome/browser/predictors/resource_prefetch_predictor_browsertest.cc b/chrome/browser/predictors/resource_prefetch_predictor_browsertest.cc
index 4b6a681486df0d4ab3f1f84052205bd135eed63a..e1a8a60e0adccd0d939d1944bf263c0eb7629eb2 100644
--- a/chrome/browser/predictors/resource_prefetch_predictor_browsertest.cc
+++ b/chrome/browser/predictors/resource_prefetch_predictor_browsertest.cc
@@ -9,6 +9,7 @@
 #include "base/command_line.h"
 #include "base/memory/ptr_util.h"
 #include "base/strings/string_util.h"
+#include "base/test/histogram_tester.h"
 #include "chrome/browser/browsing_data/browsing_data_helper.h"
 #include "chrome/browser/browsing_data/browsing_data_remover.h"
 #include "chrome/browser/browsing_data/browsing_data_remover_factory.h"
@@ -271,7 +272,9 @@ class PrefetchingObserver : public TestObserver {
     ADD_FAILURE() << "Prefetching shouldn't activate learning";
   }
 
-  void OnPrefetchingFinished(const GURL& main_frame_url) override {
+  void OnPrefetchingFinished(
+      const GURL& main_frame_url,
+      const ResourcePrefetcher::PrefetcherStats& stats) override {
     EXPECT_EQ(main_frame_url_, main_frame_url);
     run_loop_.Quit();
   }
@@ -317,6 +320,7 @@ class ResourcePrefetchPredictorBrowserTest : public InProcessBrowserTest {
         ResourcePrefetchPredictorFactory::GetForProfile(browser()->profile());
     ASSERT_TRUE(predictor_);
     EnsurePredictorInitialized();
+    histogram_tester_.reset(new base::HistogramTester());
   }
 
   void TestLearningAndPrefetching(const GURL& main_frame_url) {
@@ -599,6 +603,10 @@ class ResourcePrefetchPredictorBrowserTest : public InProcessBrowserTest {
     else
       http_response->AddCustomHeader("Cache-Control", "max-age=2147483648");
 
+    // Add some content, otherwise the prefetch size histogram rounds down to
+    // 0kB.
+    http_response->set_content(std::string(1024, static_cast<char>(42)));

[alexilin, 2017/02/09 15:24:17]

It will cause additional parsing errors in tests. But whatever...

[Benoit L, 2017/02/13 16:13:15]

Changed to a space, which should be fine for the various text resources.
Done.

+
     return std::move(http_response);
   }
 
@@ -624,6 +632,10 @@ class ResourcePrefetchPredictorBrowserTest : public InProcessBrowserTest {
     return ++visit_count_[main_frame_url];
   }
 
+ protected:
+  std::unique_ptr<base::HistogramTester> histogram_tester_;

[alexilin, 2017/02/09 15:24:18]

Could you put it at the end of (first) protected section?
https://google.github.io/styleguide/cppguide.html#Declaration_Order

[Benoit L, 2017/02/13 16:13:15]

Done.

+
+ private:
   ResourcePrefetchPredictor* predictor_;
   std::unique_ptr<net::EmbeddedTestServer> https_server_;
   std::map<GURL, ResourceSummary> resources_;
@@ -642,6 +654,22 @@ IN_PROC_BROWSER_TEST_F(ResourcePrefetchPredictorBrowserTest, Simple) {
   AddResource(GetURL(kFontPath), content::RESOURCE_TYPE_FONT_RESOURCE,
               net::HIGHEST);
   TestLearningAndPrefetching(GetURL(kHtmlSubresourcesPath));
+
+  // The local cache is cleared.
+  histogram_tester_->ExpectBucketCount(
+      internal::kResourcePrefetchPredictorPrefetchMissesCountCached, 0, 1);
+  histogram_tester_->ExpectBucketCount(
+      internal::kResourcePrefetchPredictorPrefetchMissesCountNotCached, 0, 1);
+  histogram_tester_->ExpectBucketCount(
+      internal::kResourcePrefetchPredictorPrefetchHitsCountCached, 0, 1);
+  histogram_tester_->ExpectBucketCount(
+      internal::kResourcePrefetchPredictorPrefetchHitsCountNotCached, 4, 1);
+
+  histogram_tester_->ExpectBucketCount(
+      internal::kResourcePrefetchPredictorPrefetchMissesSize, 0, 1);
+  // Each request is ~1k, see HandleResourceRequest() above.
+  histogram_tester_->ExpectBucketCount(
+      internal::kResourcePrefetchPredictorPrefetchHitsSize, 4, 1);
 }
 
 IN_PROC_BROWSER_TEST_F(ResourcePrefetchPredictorBrowserTest, Redirect) {