Add a new Chromium feature for partial style recalc after font loading

This patch adds a new Chromium feature to control the Blink runtime
enabled feature CSSReducedFontLoadingInvalidations. This allows us to
study performance impacts of the feature via finch experiments.

Bug: 441925
Change-Id: Icba6f1f1899af0bcecc12cf570786a07364f4fab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2040616Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738864}

content/child/runtime_features.cc

@@ -358,6 +358,9 @@ void SetRuntimeFeaturesFromChromiumFeatures() {
            kEnableOnly},
           {"HTMLImports", blink::features::kWebComponentsV0Enabled,
            kEnableOnly},
+          {"CSSReducedFontLoadingInvalidations",
+           blink::features::kCSSReducedFontLoadingInvalidations,
+           kUseFeatureState},
 
       };
   for (const auto& mapping : runtimeFeatureNameToChromiumFeatureMapping) {

third_party/blink/common/features.cc

@@ -453,5 +453,8 @@ const base::Feature kLowLatencyWebGLSwapChain{"LowLatencyWebGLSwapChain",
 const base::Feature kForceExtraRenderingToTrackStickyFrame{
     "ForceExtraRenderingToTrackStickyFrame", base::FEATURE_DISABLED_BY_DEFAULT};
 
+const base::Feature kCSSReducedFontLoadingInvalidations{
+    "CSSReducedFontLoadingInvalidations", base::FEATURE_DISABLED_BY_DEFAULT};
+
 }  // namespace features
 }  // namespace blink

third_party/blink/public/common/features.h

@@ -146,6 +146,9 @@ BLINK_COMMON_EXPORT extern const base::Feature kLowLatencyWebGLSwapChain;
 BLINK_COMMON_EXPORT extern const base::Feature
     kForceExtraRenderingToTrackStickyFrame;
 
+BLINK_COMMON_EXPORT extern const base::Feature
+    kCSSReducedFontLoadingInvalidations;
+
 }  // namespace features
 }  // namespace blink