Limit the number of page hints that can be loaded to the memory

The threshold is controlled using field trial.
Also, add few more histograms to track any regressions.

Change-Id: I7901f70196dd23de5eec6fc9574602c71fbe0235
Bug: 882913
Reviewed-on: https://chromium-review.googlesource.com/1214748
Commit-Queue: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Doug Arnett <dougarnett@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590550}

components/previews/content/previews_hints.cc

@@ -176,6 +176,8 @@ std::unique_ptr<PreviewsHints> PreviewsHints::CreateFromConfig(
   url_matcher::URLMatcherConditionSet::Vector all_conditions;
   std::set<std::string> seen_host_suffixes;
 
+  size_t total_resource_loading_hints_received = 0;
+  size_t total_page_patterns_with_resource_loading_hints_received = 0;
   // Process hint configuration.
   for (const auto hint : config.hints()) {
     // We only support host suffixes at the moment. Skip anything else.
@@ -223,9 +225,37 @@ std::unique_ptr<PreviewsHints> PreviewsHints::CreateFromConfig(
     if (ShouldProcessPageHints() && !hint.page_hints().empty()) {
       UMA_HISTOGRAM_COUNTS("ResourceLoadingHints.PageHints.ProcessedCount",
                            hint.page_hints().size());
-      hints->initial_hints_.push_back(hint);
+
+      for (const auto& page_hint : hint.page_hints()) {
+        for (const auto& optimization : page_hint.whitelisted_optimizations()) {
+          base::Optional<PreviewsType> previews_type =
+              ConvertProtoOptimizationTypeToPreviewsOptimizationType(
+                  optimization.optimization_type());
+
+          if (!previews_type ||
+              previews_type != PreviewsType::RESOURCE_LOADING_HINTS) {
+            continue;
+          }
+          total_page_patterns_with_resource_loading_hints_received++;
+          total_resource_loading_hints_received +=
+              optimization.resource_loading_hints().size();
+        }
+      }
+
+      if (total_page_patterns_with_resource_loading_hints_received <=
+          previews::params::GetMaxPageHintsInMemoryThreshhold()) {
+        hints->initial_hints_.push_back(hint);
+      }
     }
   }
+  if (ShouldProcessPageHints()) {
+    UMA_HISTOGRAM_COUNTS_100000(
+        "ResourceLoadingHints.ResourceHints.TotalReceived",
+        total_resource_loading_hints_received);
+    UMA_HISTOGRAM_COUNTS_1000(
+        "ResourceLoadingHints.PageHints.TotalReceived",
+        total_page_patterns_with_resource_loading_hints_received);
+  }
   hints->url_matcher_.AddConditionSets(all_conditions);
 
   // Completed processing hints data without crashing so clear sentinel.

components/previews/core/previews_experiments.cc

@@ -245,6 +245,12 @@ int ResourceLoadingHintsVersion() {
                                           kVersion, 0);
 }
 
+size_t GetMaxPageHintsInMemoryThreshhold() {
+  return GetFieldTrialParamByFeatureAsInt(features::kResourceLoadingHints,
+                                          "max_page_hints_in_memory_threshold",
+                                          500);
+}
+
 bool IsOptimizationHintsEnabled() {
   return base::FeatureList::IsEnabled(features::kOptimizationHints);
 }

components/previews/core/previews_experiments.h

@@ -128,6 +128,9 @@ int LitePageServerPreviewsVersion();
 int NoScriptPreviewsVersion();
 int ResourceLoadingHintsVersion();
 
+// The maximum number of page hints that should be loaded to memory.
+size_t GetMaxPageHintsInMemoryThreshhold();
+
 // Whether server optimization hints are enabled.
 bool IsOptimizationHintsEnabled();
 

tools/metrics/histograms/histograms.xml

@@ -84999,6 +84999,30 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="ResourceLoadingHints.PageHints.TotalReceived"
+    units="total page hints count">
+  <owner>tbansal@chromium.org</owner>
+  <summary>
+    The total count of page hints received by the browser from the component
+    updater. Only the page hints that have at least one resource loading hint
+    are counted. One sample is recorded every time optimization guide service
+    processes the optimization hints provided by the component updater. The
+    count of hints loaded to memory may be lower than this.
+  </summary>
+</histogram>
+
+<histogram name="ResourceLoadingHints.ResourceHints.TotalReceived"
+    units="total resource loading hints count">
+  <owner>tbansal@chromium.org</owner>
+  <summary>
+    The total count of resource loading hints across all page hints received by
+    the browser from the component updater. One sample is recorded every time
+    optimization guide service processes the optimization hints provided by the
+    component updater. The count of hints loaded to memory may be lower than
+    this.
+  </summary>
+</histogram>
+
 <histogram name="ResourceLoadingHints.ResourceLoadingBlocked"
     units="loading blocked">
   <owner>tbansal@chromium.org</owner>