Add UKM for max JS Bytes

Captures maximum decoded byte sizes of all JS resources per page load.

Bug: 1033626
Change-Id: Ib4717fcdcfab6cdc81f8a0416dc3227643a5fdd4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2005812
Commit-Queue: Rodney Ding <rodneyding@google.com>
Reviewed-by: John Delaney <johnidel@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Jason Chase <chasej@chromium.org>
Reviewed-by: Timothy Dresser <tdresser@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735910}

chrome/browser/page_load_metrics/observers/ukm_page_load_metrics_observer.cc

@@ -230,6 +230,8 @@ void UkmPageLoadMetricsObserver::OnResourceDataUseObserved(
       continue;
     if (blink::IsSupportedJavascriptMimeType(resource->mime_type)) {
       js_decoded_bytes_ += resource->decoded_body_length;
+      if (resource->decoded_body_length > js_max_decoded_bytes_)
+        js_max_decoded_bytes_ = resource->decoded_body_length;
     }
     if (resource->cache_type !=
         page_load_metrics::mojom::CacheType::kNotCached) {
@@ -362,6 +364,8 @@ void UkmPageLoadMetricsObserver::RecordTimingMetrics(
   // Use a bucket spacing factor of 10 for JS bytes.
   builder.SetNet_JavaScriptBytes(
       ukm::GetExponentialBucketMin(js_decoded_bytes_, 10));
+  builder.SetNet_JavaScriptMaxBytes(
+      ukm::GetExponentialBucketMin(js_max_decoded_bytes_, 10));
 
   if (main_frame_timing_)
     ReportMainResourceTimingMetrics(timing, &builder);

chrome/browser/page_load_metrics/observers/ukm_page_load_metrics_observer.h

@@ -137,6 +137,9 @@ class UkmPageLoadMetricsObserver
   // Sum of decoded body lengths of JS resources in bytes.
   int64_t js_decoded_bytes_ = 0;
 
+  // Max decoded body length of JS resources in bytes.
+  int64_t js_max_decoded_bytes_ = 0;
+
   // Network quality estimates.
   net::EffectiveConnectionType effective_connection_type_ =
       net::EFFECTIVE_CONNECTION_TYPE_UNKNOWN;

chrome/browser/page_load_metrics/observers/ukm_page_load_metrics_observer_unittest.cc

@@ -1213,7 +1213,7 @@ TEST_F(UkmPageLoadMetricsObserverTest, JSSizeMetrics) {
   DeleteContents();
 
   // Metrics look at decoded body length.
-  // 30 + 50 = 80 kilobytes
+  // 30 + 50 = 80 kilobytes.
   int64_t bucketed_network_js_bytes =
       ukm::GetExponentialBucketMin(80 * 1024, 10);
 
@@ -1230,6 +1230,57 @@ TEST_F(UkmPageLoadMetricsObserverTest, JSSizeMetrics) {
   }
 }
 
+TEST_F(UkmPageLoadMetricsObserverTest, JSMaxSizeMetrics) {
+  NavigateAndCommit(GURL(kTestUrl1));
+
+  std::vector<page_load_metrics::mojom::ResourceDataUpdatePtr> resources;
+
+  // 30 kilobytes after decoding.
+  resources.push_back(CreateResource(true /* was_cached */, 0 /* delta_bytes */,
+                                     20 * 1024 /* encoded_body_length */,
+                                     30 * 1024 /* decoded_body_length */,
+                                     true /* is_complete */));
+
+  // 500 kilobytes after decoding.
+  resources.push_back(CreateResource(
+      false /* was_cached */, 400 * 1024 /* delta_bytes */,
+      400 * 1024 /* encoded_body_length */,
+      500 * 1024 /* decoded_body_length */, true /* is_complete */));
+
+  // 120 kilobytes after decoding, not JS.
+  resources.push_back(CreateResource(
+      false /* was_cached */, 40 * 1024 /* delta_bytes */,
+      100 * 1024 /* encoded_body_length */,
+      120 * 1024 /* decoded_body_length */, true /* is_complete */));
+
+  resources[0]->mime_type = "application/javascript";
+  resources[1]->mime_type = "application/javascript";
+  resources[2]->mime_type = "test";
+
+  tester()->SimulateResourceDataUseUpdate(resources);
+
+  // Simulate closing the tab.
+  DeleteContents();
+
+  // Metrics look at max decoded body length.
+  // max(30,500) = 500 kilobytes.
+  int64_t bucketed_network_js_max_bytes =
+      ukm::GetExponentialBucketMin(500 * 1024, 10);
+
+  std::map<ukm::SourceId, ukm::mojom::UkmEntryPtr> merged_entries =
+      tester()->test_ukm_recorder().GetMergedEntriesByName(
+          PageLoad::kEntryName);
+  EXPECT_EQ(1ul, merged_entries.size());
+
+  for (const auto& kv : merged_entries) {
+    tester()->test_ukm_recorder().ExpectEntrySourceHasUrl(kv.second.get(),
+                                                          GURL(kTestUrl1));
+    tester()->test_ukm_recorder().ExpectEntryMetric(
+        kv.second.get(), "Net.JavaScriptMaxBytes",
+        bucketed_network_js_max_bytes);
+  }
+}
+
 TEST_F(UkmPageLoadMetricsObserverTest, CpuTimeMetrics) {
   NavigateAndCommit(GURL(kTestUrl1));
 

tools/metrics/ukm/ukm.xml

@@ -6956,6 +6956,14 @@ be describing additional metrics about the same event.
       bytes up until the page/app is backgrounded.
     </summary>
   </metric>
+  <metric name="Net.JavaScriptMaxBytes">
+    <summary>
+      The max of decoded body lengths of all JavaScript resouces that completed
+      loading on the page. This is rounded down to the nearest exponential
+      bucket (with a bucket spacing factor of 10). On mobile this only records
+      bytes up until the page/app is backgrounded.
+    </summary>
+  </metric>
   <metric name="Net.NetworkBytes">
     <obsolete>
       Deprecated 03/2019 in favor of Net.NetworkBytes2.