Fix class names for prototypes

Per Web IDL specification.

Author: TimothyGu

src/headers.js

@@ -61,6 +61,13 @@ export default class Headers {
 				this.append(prop, headers[prop]);
 			}
 		}
+
+		Object.defineProperty(this, Symbol.toStringTag, {
+			value: 'Headers',
+			writable: false,
+			enumerable: false,
+			configurable: true
+		});
 	}
 
 	/**
@@ -222,13 +229,13 @@ export default class Headers {
 	[Symbol.iterator]() {
 		return this.entries();
 	}
-
-	/**
-	 * Tag used by `Object.prototype.toString()`.
-	 */
-	get [Symbol.toStringTag]() {
-		return 'Headers';
-	}
 }
 
+Object.defineProperty(Headers.prototype, Symbol.toStringTag, {
+	value: 'HeadersPrototype',
+	writable: false,
+	enumerable: false,
+	configurable: true
+});
+
 Headers.FOLLOW_SPEC = false;

src/request.js

@@ -58,6 +58,13 @@ export default class Request extends Body {
 
 		// server request options
 		Object.assign(this, parsedURL);
+
+		Object.defineProperty(this, Symbol.toStringTag, {
+			value: 'Request',
+			writable: false,
+			enumerable: false,
+			configurable: true
+		});
 	}
 
 	get url() {
@@ -72,11 +79,11 @@ export default class Request extends Body {
 	clone() {
 		return new Request(this);
 	}
-
-	/**
-	 * Tag used by `Object.prototype.toString()`.
-	 */
-	get [Symbol.toStringTag]() {
-		return 'Request';
-	}
 }
+
+Object.defineProperty(Request.prototype, Symbol.toStringTag, {
+	value: 'RequestPrototype',
+	writable: false,
+	enumerable: false,
+	configurable: true
+});

src/response.js

@@ -24,6 +24,13 @@ export default class Response extends Body {
 		this.status = opts.status || 200;
 		this.statusText = opts.statusText || STATUS_CODES[this.status];
 		this.headers = new Headers(opts.headers);
+
+		Object.defineProperty(this, Symbol.toStringTag, {
+			value: 'Response',
+			writable: false,
+			enumerable: false,
+			configurable: true
+		});
 	}
 
 	/**
@@ -49,11 +56,11 @@ export default class Response extends Body {
 		});
 
 	}
-
-	/**
-	 * Tag used by `Object.prototype.toString()`.
-	 */
-	get [Symbol.toStringTag]() {
-		return 'Response';
-	}
 }
+
+Object.defineProperty(Response.prototype, Symbol.toStringTag, {
+	value: 'ResponsePrototype',
+	writable: false,
+	enumerable: false,
+	configurable: true
+});