Record local histogram when component hints are updated

Bug: 986438
Change-Id: Ie2c45b4b192c97f106ffa157f7ab1dcce47a8e6b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1719408
Commit-Queue: Sophie Chang <sophiechang@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#681107}

components/optimization_guide/hints_component_util.cc

@@ -29,6 +29,9 @@ void MaybePopulateProcessHintsComponentResult(
 
 }  // namespace
 
+const char kComponentHintsUpdatedResultHistogramString[] =
+    "OptimizationGuide.UpdateComponentHints.Result";
+
 void RecordProcessHintsComponentResult(ProcessHintsComponentResult result) {
   UMA_HISTOGRAM_ENUMERATION(kProcessHintsComponentResultHistogramString,
                             result);

components/optimization_guide/hints_component_util.h

@@ -13,6 +13,10 @@ namespace optimization_guide {
 
 struct HintsComponentInfo;
 
+// The local histogram used to record that the component hints are stored in
+// the cache and are ready for use.
+extern const char kComponentHintsUpdatedResultHistogramString[];
+
 // Enumerates the possible outcomes of processing the hints component.
 //
 // Used in UMA histograms, so the order of enumerators should not be changed.

components/previews/content/previews_optimization_guide.cc

@@ -8,6 +8,7 @@
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "base/metrics/histogram_macros.h"
+#include "base/metrics/histogram_macros_local.h"
 #include "base/rand_util.h"
 #include "base/task/post_task.h"
 #include "base/task_runner_util.h"
@@ -15,6 +16,7 @@
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_settings.h"
 #include "components/optimization_guide/hint_cache_store.h"
 #include "components/optimization_guide/hints_component_info.h"
+#include "components/optimization_guide/hints_component_util.h"
 #include "components/optimization_guide/hints_fetcher.h"
 #include "components/optimization_guide/optimization_guide_features.h"
 #include "components/optimization_guide/optimization_guide_prefs.h"
@@ -328,6 +330,13 @@ void PreviewsOptimizationGuide::OnHintsUpdated(
     base::OnceClosure update_closure) {
   DCHECK(ui_task_runner_->BelongsToCurrentThread());
   DCHECK(pref_service_);
+
+  // Record the result of updating the hints. This is used as a signal for the
+  // hints being fully processed in release tools and testing.
+  LOCAL_HISTOGRAM_BOOLEAN(
+      optimization_guide::kComponentHintsUpdatedResultHistogramString,
+      hints_ != nullptr);
+
   if (!update_closure.is_null())
     std::move(update_closure).Run();
 

components/previews/content/previews_optimization_guide_unittest.cc

@@ -244,12 +244,21 @@ class PreviewsOptimizationGuideTest
 
   void ProcessHints(const optimization_guide::proto::Configuration& config,
                     const std::string& version) {
+    base::HistogramTester histogram_tester;
+
     optimization_guide::HintsComponentInfo info(
         base::Version(version),
         temp_dir().Append(FILE_PATH_LITERAL("somefile.pb")));
     ASSERT_NO_FATAL_FAILURE(WriteConfigToFile(config, info.path));
+    base::RunLoop run_loop;
+    guide_->ListenForNextUpdateForTesting(run_loop.QuitClosure());
     guide_->OnHintsComponentAvailable(info);
-    RunUntilIdle();
+    run_loop.Run();
+
+    // Check for histogram to ensure that we do not remove this histogram since
+    // it's relied on in release tools.
+    histogram_tester.ExpectTotalCount(
+        "OptimizationGuide.UpdateComponentHints.Result", 1);
   }
 
   void EnableDataSaver() {