Add an arm to the lightweight no state prefetch experiment

This adds an arm to separate async vs sync script, so we can see if
there is a big effect when NoState prefetching async script.

Bug: 93446
Change-Id: Ic04a30b2af3ee0517dca88d5cbb754d619003f45
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1707054Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680186}

chrome/browser/prerender/prerender_nostate_prefetch_browsertest.cc

@@ -320,6 +320,7 @@ IN_PROC_BROWSER_TEST_F(NoStatePrefetchBrowserTest, PrefetchAllResourceTypes) {
   WaitForRequestCount(src_server()->GetURL(kPrefetchPageMultipleResourceTypes),
                       1);
   WaitForRequestCount(src_server()->GetURL(kPrefetchScript), 1);
+  WaitForRequestCount(src_server()->GetURL(kPrefetchScript2), 1);
   WaitForRequestCount(src_server()->GetURL(kPrefetchPng), 1);
   WaitForRequestCount(src_server()->GetURL(kPrefetchCss), 1);
   WaitForRequestCount(src_server()->GetURL(kPrefetchFont), 1);
@@ -351,6 +352,7 @@ IN_PROC_BROWSER_TEST_F(HTMLOnlyNoStatePrefetchBrowserTest, PrefetchHTMLOnly) {
   WaitForRequestCount(src_server()->GetURL(kPrefetchPageMultipleResourceTypes),
                       1);
   WaitForRequestCount(src_server()->GetURL(kPrefetchScript), 0);
+  WaitForRequestCount(src_server()->GetURL(kPrefetchScript2), 0);
   WaitForRequestCount(src_server()->GetURL(kPrefetchPng), 0);
   WaitForRequestCount(src_server()->GetURL(kPrefetchCss), 0);
   WaitForRequestCount(src_server()->GetURL(kPrefetchFont), 0);
@@ -384,6 +386,43 @@ IN_PROC_BROWSER_TEST_F(HTMLCSSNoStatePrefetchBrowserTest, PrefetchHTMLCSS) {
   WaitForRequestCount(src_server()->GetURL(kPrefetchPageMultipleResourceTypes),
                       1);
   WaitForRequestCount(src_server()->GetURL(kPrefetchScript), 0);
+  WaitForRequestCount(src_server()->GetURL(kPrefetchScript2), 0);
+  WaitForRequestCount(src_server()->GetURL(kPrefetchPng), 0);
+  WaitForRequestCount(src_server()->GetURL(kPrefetchCss), 1);
+  WaitForRequestCount(src_server()->GetURL(kPrefetchFont), 0);
+}
+
+// Test and Test Class for lightweight prefetch under the HTML+CSS+SyncScript
+// configuration.
+class HTMLCSSSyncScriptNoStatePrefetchBrowserTest
+    : public NoStatePrefetchBrowserTest {
+ public:
+  void SetUp() override {
+    std::map<std::string, std::string> parameters;
+    parameters["skip_other"] = "true";
+    parameters["skip_async_script"] = "true";
+    feature_list_.InitWithFeaturesAndParameters(
+        {{blink::features::kLightweightNoStatePrefetch, parameters}}, {});
+    NoStatePrefetchBrowserTest::SetUp();
+  }
+
+ private:
+  base::test::ScopedFeatureList feature_list_;
+};
+
+// Checks that the expected resource types are fetched via NoState Prefetch.
+IN_PROC_BROWSER_TEST_F(HTMLCSSSyncScriptNoStatePrefetchBrowserTest,
+                       PrefetchHTMLCSSSyncScript) {
+  std::unique_ptr<TestPrerender> test_prerender =
+      PrefetchFromFile(kPrefetchPageMultipleResourceTypes,
+                       FINAL_STATUS_NOSTATE_PREFETCH_FINISHED);
+
+  // Verify that the page load did not happen.
+  test_prerender->WaitForLoads(0);
+  WaitForRequestCount(src_server()->GetURL(kPrefetchPageMultipleResourceTypes),
+                      1);
+  WaitForRequestCount(src_server()->GetURL(kPrefetchScript), 1);
+  WaitForRequestCount(src_server()->GetURL(kPrefetchScript2), 0);
   WaitForRequestCount(src_server()->GetURL(kPrefetchPng), 0);
   WaitForRequestCount(src_server()->GetURL(kPrefetchCss), 1);
   WaitForRequestCount(src_server()->GetURL(kPrefetchFont), 0);
@@ -418,6 +457,7 @@ IN_PROC_BROWSER_TEST_F(HTMLCSSScriptNoStatePrefetchBrowserTest,
   WaitForRequestCount(src_server()->GetURL(kPrefetchPageMultipleResourceTypes),
                       1);
   WaitForRequestCount(src_server()->GetURL(kPrefetchScript), 1);
+  WaitForRequestCount(src_server()->GetURL(kPrefetchScript2), 1);
   WaitForRequestCount(src_server()->GetURL(kPrefetchPng), 0);
   WaitForRequestCount(src_server()->GetURL(kPrefetchCss), 1);
   WaitForRequestCount(src_server()->GetURL(kPrefetchFont), 0);

chrome/test/data/prerender/prefetch_page_multiple_resource_types.html

 <html>
 <body>
   <script src="prefetch.js"></script>
+  <script src="prefetch2.js" async></script>
   <img src="image.png"/>
   <link rel="prefetch" href="prefetch.html">
   <link rel="stylesheet" type="text/css" href="style.css"/>

third_party/blink/renderer/core/html/parser/html_resource_preloader.cc

@@ -115,27 +115,25 @@ bool HTMLResourcePreloader::AllowPreloadRequest(PreloadRequest* preload) const {
     case ResourceType::kVideo:
     case ResourceType::kManifest:
     case ResourceType::kMock:
-      if (GetFieldTrialParamByFeatureAsBool(
-              features::kLightweightNoStatePrefetch, "skip_other", false)) {
-        return false;
-      }
-      break;
+      return !GetFieldTrialParamByFeatureAsBool(
+          features::kLightweightNoStatePrefetch, "skip_other", false);
     case ResourceType::kImage:
       return false;
     case ResourceType::kCSSStyleSheet:
-      break;
+      return true;
     case ResourceType::kScript:
+      // We might skip all script.
       if (GetFieldTrialParamByFeatureAsBool(
               features::kLightweightNoStatePrefetch, "skip_script", false)) {
-        // TODO(ryansturm): Add an arm to block async script only.
-        // https://crbug.com/934466
         return false;
       }
-      break;
-  }
 
-  // Skip lazy-loaded resources.
-  return preload->DeferOption() == FetchParameters::DeferOption::kNoDefer;
+      // Otherwise, we might skip async/deferred script.
+      return !GetFieldTrialParamByFeatureAsBool(
+                 features::kLightweightNoStatePrefetch, "skip_async_script",
+                 false) ||
+             preload->DeferOption() == FetchParameters::DeferOption::kNoDefer;
+  }
 }
 
 }  // namespace blink