Cherry-pick 7a77efe. rdar://123268364

    Unprefixed backdrop filter should only be enabled when UNPREFIXED_BACKDROP_FILTER is true.
    https://bugs.webkit.org/show_bug.cgi?id=269755
    <rdar://123268364>

    Reviewed by Tim Nguyen.

    * Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml:
    * Source/WebKit/Shared/WebPreferencesDefaultValues.h:

    Canonical link: https://commits.webkit.org/275088@main

Identifier: 274471.486@safari-7619.1.5-branch

Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml

@@ -1511,20 +1511,20 @@ CSSTypedOMEnabled:
 
 CSSUnprefixedBackdropFilterEnabled:
   type: bool
-  status: embedder
+  status: Backdropfilter_feature_status
   category: css
   humanReadableName: "CSS Unprefixed Backdrop Filter"
   humanReadableDescription: "Enable unprefixed backdrop-filter CSS property"
   defaultValue:
     WebKitLegacy:
       "ENABLE(UNPREFIXED_BACKDROP_FILTER)": true
-      default: true
+      default: false
     WebKit:
       "ENABLE(UNPREFIXED_BACKDROP_FILTER)": true
-      default: true
+      default: false
     WebCore:
       "ENABLE(UNPREFIXED_BACKDROP_FILTER)": true
-      default: true
+      default: false
 
 CSSWordBreakAutoPhraseEnabled:
   type: bool

Source/WebKit/Shared/WebPreferencesDefaultValues.h

@@ -40,6 +40,12 @@
 #define Webgpu_feature_status Preview
 #endif
 
+#if defined(ENABLE_UNPREFIXED_BACKDROP_FILTER) && ENABLE_UNPREFIXED_BACKDROP_FILTER
+#define Backdropfilter_feature_status Stable
+#else
+#define Backdropfilter_feature_status Testable
+#endif
+
 namespace WebKit {
 
 #if PLATFORM(IOS_FAMILY)

Tools/DumpRenderTree/TestOptions.cpp

@@ -67,6 +67,7 @@ const TestFeatures& TestOptions::defaults()
             // These are non-experimental WebPreference values that must always be set as they
             // differ from the default set in the WebPreferences*.yaml configuration.
             { "AllowsInlineMediaPlayback", true },
+            { "CSSUnprefixedBackdropFilterEnabled", true },
             { "CanvasUsesAcceleratedDrawing", true },
             { "ColorFilterEnabled", true },
             { "CustomPasteboardDataEnabled", true },

Tools/WebKitTestRunner/TestOptions.cpp

@@ -81,6 +81,7 @@ const TestFeatures& TestOptions::defaults()
             { "BroadcastChannelOriginPartitioningEnabled", false },
             { "BuiltInNotificationsEnabled", false },
             { "CSSOMViewScrollingAPIEnabled", true },
+            { "CSSUnprefixedBackdropFilterEnabled", true },
             { "CaptureAudioInGPUProcessEnabled", captureAudioInGPUProcessEnabledValue },
             { "CaptureAudioInUIProcessEnabled", false },
             { "CaptureVideoInGPUProcessEnabled", captureVideoInGPUProcessEnabledValue },