Add a heartbeat to web socket connections

This prevents them from being killed when they are idle.  To test run behind
NGINX, make sure the sockets are idle (check dev tools), then wait 60+ seconds.

Index: code-server/lib/vscode/src/vs/base/parts/ipc/common/ipc.net.ts
===================================================================
--- code-server.orig/lib/vscode/src/vs/base/parts/ipc/common/ipc.net.ts
+++ code-server/lib/vscode/src/vs/base/parts/ipc/common/ipc.net.ts
@@ -7,6 +7,7 @@ import { VSBuffer } from 'vs/base/common
 import { Emitter, Event } from 'vs/base/common/event';
 import { Disposable, dispose, IDisposable } from 'vs/base/common/lifecycle';
 import { IIPCLogger, IMessagePassingProtocol, IPCClient } from 'vs/base/parts/ipc/common/ipc';
+import { isWeb } from 'vs/base/common/platform';
 
 export const enum SocketDiagnosticsEventType {
 	Created = 'created',
@@ -828,6 +829,19 @@ export class PersistentProtocol implemen
 		this._socketDisposables.push(this._socketWriter);
 		this._socketReader = new ProtocolReader(this._socket);
 		this._socketDisposables.push(this._socketReader);
+		// Send empty messages to keep the socket alive.  We only need this on the
+		// web where sockets can be killed by reverse proxies for inactivity.
+		if (isWeb) {
+			const timer = setInterval(() => {
+				const msg = new ProtocolMessage(ProtocolMessageType.None, 0, 0, getEmptyBuffer());
+				this._socketWriter.write(msg);
+			}, 45000); // NGINX has a 60 second default timeout so try 45 seconds.
+			this._socketDisposables.push({
+				dispose: () => {
+					clearInterval(timer);
+				},
+			});
+		}
 		this._socketDisposables.push(this._socketReader.onMessage(msg => this._receiveMessage(msg)));
 		this._socketDisposables.push(this._socket.onClose((e) => this._onSocketClose.fire(e)));
 		if (initialChunk) {