Small font UKM should be disabled by default under performance issue

Bug: 1159296
Change-Id: I0af37949004a85479d41b5e2929a735637264c1b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2626620
Commit-Queue: Hiroki Kumazaki <kumagi@google.com>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843495}

third_party/blink/renderer/core/mobile_metrics/mobile_friendliness_checker.cc

@@ -17,7 +17,7 @@
 namespace blink {
 
 const base::Feature kSmallTextRatio{"SmallTextRatio",
-                                    base::FEATURE_ENABLED_BY_DEFAULT};
+                                    base::FEATURE_DISABLED_BY_DEFAULT};
 
 MobileFriendlinessChecker::MobileFriendlinessChecker(LocalFrameView& frame_view)
     : frame_view_(&frame_view),

third_party/blink/renderer/core/mobile_metrics/mobile_friendliness_checker_test.cc

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "third_party/blink/renderer/core/mobile_metrics/mobile_friendliness_checker.h"
+#include "base/test/scoped_feature_list.h"
 #include "third_party/blink/public/common/mobile_metrics/mobile_friendliness.h"
 #include "third_party/blink/public/web/web_settings.h"
 #include "third_party/blink/renderer/core/frame/frame_test_helpers.h"
@@ -20,6 +21,10 @@ class MobileFriendlinessCheckerTest : public testing::Test {
     url_test_helpers::UnregisterAllURLsAndClearMemoryCache();
   }
 
+  void SetUp() override {
+    scoped_feature_list_.InitAndEnableFeature(kSmallTextRatio);
+  }
+
   static void ConfigureAndroidSettings(WebSettings* settings) {
     settings->SetViewportEnabled(true);
     settings->SetViewportMetaEnabled(true);
@@ -68,6 +73,9 @@ class MobileFriendlinessCheckerTest : public testing::Test {
     }
     return web_frame_client.GetMobileFriendliness();
   }
+
+ private:
+  base::test::ScopedFeatureList scoped_feature_list_;
 };
 
 TEST_F(MobileFriendlinessCheckerTest, NoViewportSetting) {