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..46ddbb41223b6fb7a6fc2d036309231964292367 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"
@@ -76,7 +77,6 @@ struct ResourceSummary {
         is_prohibited(false) {}
 
   ResourcePrefetchPredictor::URLRequestSummary request;
-  std::string content;
   // Allows to update HTTP ETag.
   size_t version;
   // True iff "Cache-control: no-store" header is present.
@@ -317,6 +317,7 @@ 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) {
@@ -487,6 +488,8 @@ class ResourcePrefetchPredictorBrowserTest : public InProcessBrowserTest {
     return navigation_id_history_.size();
   }
 
+  std::unique_ptr<base::HistogramTester> histogram_tester_;
+
  private:
   // ResourcePrefetchPredictor needs to be initialized before the navigation
   // happens otherwise this navigation will be ignored by predictor.
@@ -586,8 +589,6 @@ class ResourcePrefetchPredictorBrowserTest : public InProcessBrowserTest {
 
     if (!summary.request.mime_type.empty())
       http_response->set_content_type(summary.request.mime_type);
-    if (!summary.content.empty())
-      http_response->set_content(summary.content);
     if (summary.is_no_store)
       http_response->AddCustomHeader("Cache-Control", "no-store");
     if (summary.request.has_validators) {
@@ -599,6 +600,10 @@ 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, ' '));
+
     return std::move(http_response);
   }
 
@@ -642,6 +647,22 @@ 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) {