Revert "Prepare CSSKeyframesMemoryReduction for finch experiment"

This reverts commit 5b7019ed.

Reason for revert: Caused a lot of animation performance regressions

Original change's description:
> Prepare CSSKeyframesMemoryReduction for finch experiment
>
> This patch adds a Chromium feature for CSSKeyframesMemoryReduction and
> enables it in field trial testing config. This is preparation for a
> Canary/Dev finch experiment.
>
> Bug: 1141814
> Change-Id: I03c1c9beca18bdf4b286704f60b6895f60835d12
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2518097
> Reviewed-by: Steven Holte <holte@chromium.org>
> Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
> Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#824639}

TBR=chrishtr@chromium.org,holte@chromium.org,xiaochengh@chromium.org

Bug: 1141814, 1146436
Change-Id: I1a82fda304324739e0118718aad43c109641b97f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2527726
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825623}

content/child/runtime_features.cc

@@ -339,8 +339,6 @@ void SetRuntimeFeaturesFromChromiumFeatures() {
           {"BlockHTMLParserOnStyleSheets",
            blink::features::kBlockHTMLParserOnStyleSheets},
           {"CSSColorSchemeUARendering", features::kCSSColorSchemeUARendering},
-          {"CSSKeyframesMemoryReduction",
-           blink::features::kCSSKeyframesMemoryReduction},
           {"CSSReducedFontLoadingLayoutInvalidations",
            blink::features::kCSSReducedFontLoadingLayoutInvalidations},
           {"CSSMatchedPropertiesCacheDependencies",

testing/variations/fieldtrial_testing_config.json

@@ -1235,27 +1235,6 @@
             ]
         }
     ],
-    "CSSKeyframesMemoryReduction": [
-        {
-            "platforms": [
-                "android",
-                "android_weblayer",
-                "android_webview",
-                "chromeos",
-                "linux",
-                "mac",
-                "windows"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "CSSKeyframesMemoryReduction"
-                    ]
-                }
-            ]
-        }
-    ],
     "CSSMatchedPropertiesCacheDependencies": [
         {
             "platforms": [

third_party/blink/common/features.cc

@@ -808,13 +808,6 @@ const base::Feature kWebRtcLibvpxEncodeNV12{"WebRtcLibvpxEncodeNV12",
 const base::Feature kLoadingTasksUnfreezable{"LoadingTasksUnfreezable",
                                              base::FEATURE_DISABLED_BY_DEFAULT};
 
-// Changes ScopedStyleResolve and StyleEngine to use the already stored
-// StyleSheetCollection to find @keyframes rules instead of creating their
-// own hashmaps, so that we can save memory when there are web components
-// with @keyframes rules in their stylesheets.
-const base::Feature kCSSKeyframesMemoryReduction{
-    "CSSKeyframesMemoryReduction", base::FEATURE_DISABLED_BY_DEFAULT};
-
 // Kill switch for the new behavior whereby anchors with target=_blank get
 // noopener behavior by default. TODO(crbug.com/898942): Remove in Chrome 95.
 const base::Feature kTargetBlankImpliesNoOpener{

third_party/blink/public/common/features.h

@@ -334,8 +334,6 @@ BLINK_COMMON_EXPORT extern const base::Feature kWebRtcLibvpxEncodeNV12;
 
 BLINK_COMMON_EXPORT extern const base::Feature kLoadingTasksUnfreezable;
 
-BLINK_COMMON_EXPORT extern const base::Feature kCSSKeyframesMemoryReduction;
-
 BLINK_COMMON_EXPORT extern const base::Feature kTargetBlankImpliesNoOpener;
 }  // namespace features
 }  // namespace blink