WebSocket polyfill

Summary:
- Added as a library in /Libraries/WebSocket
- Drag and drop to add to project (similar to adding Geolocation polyfill)
- Exposed as `window.WebSocket` which conforms with https://developer.mozilla.org/en-US/docs/Web/API/WebSocket specs
Closes https://github.com/facebook/react-native/pull/890
Github Author: Harrison Harnisch <hharnisc@gmail.com>

Test Plan: Imported from GitHub, without a `Test Plan:` line.

Libraries/WebSocket/WebSocketBase.js

@@ -0,0 +1,97 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @providesModule WebSocketBase
+ *
+ */
+'use strict';
+
+/**
+ * Shared base for platform-specific WebSocket implementations.
+ */
+class WebSocketBase {
+  CONNECTING: number;
+  OPEN: number;
+  CLOSING: number;
+  CLOSED: number;
+
+  onclose: ?Function;
+  onerror: ?Function;
+  onmessage: ?Function;
+  onopen: ?Function;
+
+  binaryType: ?string;
+  bufferedAmount: number;
+  extension: ?string;
+  protocol: ?string;
+  readyState: number;
+  url: ?string;
+
+  constructor(url: string, protocols: ?any) {
+    this.CONNECTING = 0;
+    this.OPEN = 1;
+    this.CLOSING = 2;
+    this.CLOSED = 3;
+
+    if (!protocols) {
+      protocols = [];
+    }
+
+    this.connectToSocketImpl(url);
+  }
+
+  close(): void {
+    if (this.readyState === WebSocketBase.CLOSING ||
+        this.readyState === WebSocketBase.CLOSED) {
+      return;
+    }
+
+    if (this.readyState === WebSocketBase.CONNECTING) {
+      this.cancelConnectionImpl();
+    }
+
+    this.closeConnectionImpl();
+  }
+
+  send(data: any): void {
+    if (this.readyState === WebSocketBase.CONNECTING) {
+      throw new Error('INVALID_STATE_ERR');
+    }
+
+    if (typeof data === 'string') {
+      this.sendStringImpl(data);
+    } else if (data instanceof ArrayBuffer) {
+      this.sendArrayBufferImpl(data);
+    } else {
+      throw new Error('Not supported data type');
+    }
+  }
+
+  closeConnectionImpl(): void {
+    throw new Error('Subclass must define closeConnectionImpl method');
+  }
+
+  connectToSocketImpl(): void {
+    throw new Error('Subclass must define connectToSocketImpl method');
+  }
+
+  cancelConnectionImpl(): void {
+    throw new Error('Subclass must define cancelConnectionImpl method');
+  }
+
+  sendStringImpl(): void {
+    throw new Error('Subclass must define sendStringImpl method');
+  }
+
+  sendArrayBufferImpl(): void {
+    throw new Error('Subclass must define sendArrayBufferImpl method');
+  }
+
+}
+
+module.exports = WebSocketBase;