Remove RequireCSSExtensionForFile runtime enabled flag.

The feature has long since been stable (since M64) and doesn't seem
to be a need for this flag.

BUG=788936

Change-Id: I666390b869289c328acb4a2daa5bf4154e1702c0
Reviewed-on: https://chromium-review.googlesource.com/c/1324143Reviewed-by: Mike West <mkwst@chromium.org>
Reviewed-by: Camille Lamy <clamy@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607329}

content/child/runtime_features.cc

@@ -422,9 +422,6 @@ void SetRuntimeFeaturesDefaultsAndUpdateFromArgs(
   WebRuntimeFeatures::EnableV8ContextSnapshot(
       base::FeatureList::IsEnabled(features::kV8ContextSnapshot));
 
-  WebRuntimeFeatures::EnableRequireCSSExtensionForFile(
-      base::FeatureList::IsEnabled(features::kRequireCSSExtensionForFile));
-
   WebRuntimeFeatures::EnablePictureInPicture(
       base::FeatureList::IsEnabled(media::kPictureInPicture));
 

content/public/common/content_features.cc

@@ -351,10 +351,6 @@ const base::Feature kRasterInducingScroll{"RasterInducingScroll",
 const base::Feature kRenderingPipelineThrottling{
     "RenderingPipelineThrottling", base::FEATURE_ENABLED_BY_DEFAULT};
 
-// When loading CSS from a 'file:' URL, require a CSS-like file extension.
-const base::Feature kRequireCSSExtensionForFile{
-    "RequireCSSExtensionForFile", base::FEATURE_ENABLED_BY_DEFAULT};
-
 // Enables resampling input events on main thread.
 const base::Feature kResamplingInputEvents{"ResamplingInputEvents",
                                            base::FEATURE_DISABLED_BY_DEFAULT};

content/public/common/content_features.h

@@ -83,7 +83,6 @@ CONTENT_EXPORT extern const base::Feature kPepper3DImageChromium;
 CONTENT_EXPORT extern const base::Feature kPurgeAndSuspend;
 CONTENT_EXPORT extern const base::Feature kRasterInducingScroll;
 CONTENT_EXPORT extern const base::Feature kRenderingPipelineThrottling;
-CONTENT_EXPORT extern const base::Feature kRequireCSSExtensionForFile;
 CONTENT_EXPORT extern const base::Feature kResamplingInputEvents;
 CONTENT_EXPORT extern const base::Feature kResourceLoadScheduler;
 CONTENT_EXPORT extern const base::Feature

third_party/blink/public/platform/web_runtime_features.h

@@ -150,7 +150,6 @@ class WebRuntimeFeatures {
   BLINK_PLATFORM_EXPORT static void EnableReducedReferrerGranularity(bool);
   BLINK_PLATFORM_EXPORT static void EnableRemotePlaybackAPI(bool);
   BLINK_PLATFORM_EXPORT static void EnableRenderingPipelineThrottling(bool);
-  BLINK_PLATFORM_EXPORT static void EnableRequireCSSExtensionForFile(bool);
   BLINK_PLATFORM_EXPORT static void EnableResourceLoadScheduler(bool);
   BLINK_PLATFORM_EXPORT static void EnableScriptedSpeech(bool);
   BLINK_PLATFORM_EXPORT static void EnableScrollAnchorSerialization(bool);

third_party/blink/renderer/core/loader/resource/css_style_sheet_resource.cc

@@ -178,9 +178,7 @@ bool CSSStyleSheetResource::CanUseSheet(const CSSParserContext* parser_context,
         parser_context->CountDeprecation(
             WebFeature::kLocalCSSFileExtensionRejected);
       }
-      if (RuntimeEnabledFeatures::RequireCSSExtensionForFileEnabled()) {
-        return false;
-      }
+      return false;
     }
   }
 

third_party/blink/renderer/platform/exported/web_runtime_features.cc

@@ -440,10 +440,6 @@ void WebRuntimeFeatures::EnableRenderingPipelineThrottling(bool enable) {
   RuntimeEnabledFeatures::SetRenderingPipelineThrottlingEnabled(enable);
 }
 
-void WebRuntimeFeatures::EnableRequireCSSExtensionForFile(bool enable) {
-  RuntimeEnabledFeatures::SetRequireCSSExtensionForFileEnabled(enable);
-}
-
 void WebRuntimeFeatures::EnableResourceLoadScheduler(bool enable) {
   RuntimeEnabledFeatures::SetResourceLoadSchedulerEnabled(enable);
 }

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -1025,10 +1025,6 @@
       name: "RenderingPipelineThrottling",
       status: "stable",
     },
-    {
-      name: "RequireCSSExtensionForFile",
-      status: "stable",
-    },
     {
       name: "ResourceLoadScheduler",
       status: "experimental",