Update web-platform-tests to revision b7a8b84debb42268ea95a45bdad8f727d1facdf7

tests/wpt/web-platform-tests/shape-detection/README.md

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+The `shapedetection-helpers.js` tests require implementations of
+the `FaceDetectionTest` and `BarcodeDetectionTest` interfaces, which
+should emulate platform shape detection backends.
+
+The `FaceDetectionTest` interface is defined as:
+
+```
+  class FaceDetectionTest {
+    async initialize();  // Sets up the testing environment.
+    async reset(); // Frees the resources.
+    MockFaceDetectionProvider(); //Returns `MockFaceDetectionProvider` interface.
+  };
+
+  class MockFaceDetectionProvider {
+    getFrameData(); //Gets frame data of detection result.
+    getMaxDetectedFaces(); //Gets value of `maxDetectedFaces` in `FaceDetector` constructor
+    getFastMode(); //Gets value of `fastMode` in `FaceDetector` constructor
+  };
+```
+
+The Chromium implementation of the `FaceDetectionTest` interface is located in
+[mock-facedetection.js](../resources/chromium/mock-facedetection.js).
+
+The `BarcodeDetectionTest` interface is defined as:
+
+```
+  class BarcodeDetectionTest {
+    async initialize();  // Sets up the testing environment.
+    async reset(); // Frees the resources.
+    MockBarcodeDetectionProvider(); //Returns `MockBarcodeDetectionProvider` interface.
+  };
+
+  class MockBarcodeDetectionProvider {
+    async enumerateSupportedFormats(); //Enumerates supported formats
+    getFrameData(); //Gets frame data of detection result.
+    getFormats(); //Gets value of `formats` in `BarcodeDetector` constructor
+  };
+```
+
+The Chromium implementation of the `BarcodeDetectionTest` interface is located in
+[mock-barcodedetection.js](../resources/chromium/mock-barcodedetection.js).
+
+Other browser vendors should provide their own implementations of
+the `FaceDetectionTest` and `BarcodeDetectionTest` interfaces.