Editorial: Add CustomElementRegistry platform support

api/CustomElementRegistry.json

@@ -0,0 +1,65 @@
+{
+  "api": {
+    "CustomElementRegistry": {
+      "__compat": {
+        "mdn_url": "https://developer.mozilla.org/docs/Web/API/CustomElementRegistry",
+        "support": {
+          "webview_android": {
+            "version_added": "56",
+            "notes": "Supports 'Autonomous custom elements' but not 'Customized built-in elements'"
+          },
+          "chrome": {
+            "version_added": "54",
+            "notes": "Supports 'Autonomous custom elements' but not 'Customized built-in elements'"
+          },
+          "chrome_android": {
+            "version_added": "61",
+            "notes": "Supports 'Autonomous custom elements' but not 'Customized built-in elements'"
+          },
+          "edge": {
+            "version_added": false,
+            "notes": "Under consideration"
+          },
+          "edge_mobile": {
+            "version_added": false,
+            "notes": "Under consideration"
+          },
+          "firefox": {
+            "version_added": true,
+            "flag": {
+              "type": "preference",
+              "name": "dom.webcomponents.enabled",
+              "value_to_set": "true"
+            }
+          },
+          "ie": {
+            "version_added": false
+          },
+          "ie_mobile": {
+            "version_added": false
+          },
+          "opera": {
+            "version_added": "41",
+            "notes": "Supports 'Autonomous custom elements' but not 'Customized built-in elements'"
+          },
+          "opera_android": {
+            "version_added": false
+          },
+          "safari": {
+            "version_added": "10.1",
+            "notes": "Supports 'Autonomous custom elements' but not 'Customized built-in elements'"
+          },
+          "safari_ios": {
+            "version_added": "10.1",
+            "notes": "Supports 'Autonomous custom elements' but not 'Customized built-in elements'"
+          }
+        },
+        "status": {
+          "experimental": true,
+          "standard_track": true,
+          "deprecated": false
+        }
+      }
+    }
+  }
+}