DevTools: Ignore multiple sourceMappingUrls for external source maps

Added an edge case regression test and bugfix.

Author: Brian Vaughn

packages/react-devtools-extensions/src/__tests__/__source__/ContainingStringSourceMappingURL.js

@@ -0,0 +1,23 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+import React, {useState} from 'react';
+
+// ?sourceMappingURL=([^\s'"]+)/gm
+
+export function Component() {
+  const [count, setCount] = useState(0);
+
+  return (
+    <div>
+      <p>You clicked {count} times</p>
+      <button onClick={() => setCount(count + 1)}>Click me</button>
+    </div>
+  );
+}

packages/react-devtools-extensions/src/__tests__/__source__/__compiled__/bundle/index.js

@@ -10,6 +10,7 @@
 export {Component as ComponentWithCustomHook} from './ComponentWithCustomHook';
 export {Component as ComponentWithExternalCustomHooks} from './ComponentWithExternalCustomHooks';
 export {Component as ComponentWithMultipleHooksPerLine} from './ComponentWithMultipleHooksPerLine';
+export {Component as ContainingStringSourceMappingURL} from './ContainingStringSourceMappingURL';
 export {Component as Example} from './Example';
 export {Component as InlineRequire} from './InlineRequire';
 import * as ToDoList from './ToDoList';