Move WebFont fetching in LightweightNoStatePrefetch to its own feature

Otherwise it is impossible to roll out using the server-side
experimentations that are currently at play.

Bug: 1021749
Change-Id: Ic6bf7e48c1aba52c16ef9ed1a048af963ea187a3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1922600Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Commit-Queue: Robert Ogden <robertogden@chromium.org>
Cr-Commit-Position: refs/heads/master@{#717718}

chrome/browser/prerender/prerender_nostate_prefetch_browsertest.cc

@@ -491,14 +491,16 @@ class HTMLCSSSyncScriptFontNoStatePrefetchBrowserTest
     std::map<std::string, std::string> parameters;
     parameters["skip_other"] = "true";
     parameters["skip_async_script"] = "true";
-    parameters["skip_font"] = "false";
     feature_list_.InitWithFeaturesAndParameters(
         {{blink::features::kLightweightNoStatePrefetch, parameters}}, {});
+    fonts_feature_list_.InitAndEnableFeature(
+        blink::features::kLightweightNoStatePrefetch_FetchFonts);
     NoStatePrefetchBrowserTest::SetUp();
   }
 
  private:
   base::test::ScopedFeatureList feature_list_;
+  base::test::ScopedFeatureList fonts_feature_list_;
 };
 
 // Checks that the expected resource types are fetched via NoState Prefetch.

third_party/blink/common/features.cc

@@ -58,10 +58,8 @@ const base::Feature kDisplayLocking{"DisplayLocking",
 
 // Enable applying rounded corner masks via a GL shader rather than
 // a mask layer.
-const base::Feature kFastBorderRadius {
-  "FastBorderRadius",
-      base::FEATURE_ENABLED_BY_DEFAULT
-};
+const base::Feature kFastBorderRadius{"FastBorderRadius",
+                                      base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Enable LayoutNG.
 const base::Feature kLayoutNG{"LayoutNG", base::FEATURE_ENABLED_BY_DEFAULT};
@@ -288,6 +286,10 @@ const base::Feature kLightweightNoStatePrefetch{
 #endif
 };
 
+// A feature to enable web fonts to be fetched by No-State Prefetch.
+const base::Feature kLightweightNoStatePrefetch_FetchFonts{
+    "LightweightNoStatePrefetch_FetchFonts", base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Automatically convert light-themed pages to use a Blink-generated dark theme
 const base::Feature kForceWebContentsDarkMode{
     "WebContentsForceDark", base::FEATURE_DISABLED_BY_DEFAULT};

third_party/blink/public/common/features.h

@@ -86,6 +86,8 @@ BLINK_COMMON_EXPORT extern const base::Feature
 BLINK_COMMON_EXPORT extern const base::Feature kAudioWorkletRealtimeThread;
 
 BLINK_COMMON_EXPORT extern const base::Feature kLightweightNoStatePrefetch;
+BLINK_COMMON_EXPORT extern const base::Feature
+    kLightweightNoStatePrefetch_FetchFonts;
 
 BLINK_COMMON_EXPORT extern const base::Feature kForceWebContentsDarkMode;
 BLINK_COMMON_EXPORT extern const base::FeatureParam<ForceDarkInversionMethod>

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

@@ -123,8 +123,8 @@ bool HTMLResourcePreloader::AllowPreloadRequest(PreloadRequest* preload) const {
     case ResourceType::kCSSStyleSheet:
       return true;
     case ResourceType::kFont:
-      return !GetFieldTrialParamByFeatureAsBool(
-          features::kLightweightNoStatePrefetch, "skip_font", true);
+      return base::FeatureList::IsEnabled(
+          features::kLightweightNoStatePrefetch_FetchFonts);
     case ResourceType::kScript:
       // We might skip all script.
       if (GetFieldTrialParamByFeatureAsBool(