Init DevTools Proto (#6450)

- Create DevTools Init Proto
- Send a DevTools Init Proto when a websocket is connected.

cc: @piotrswigon @jasonwyatt

Closes #6450

COPYBARA_INTEGRATE_REVIEW=#6450 from SHeimlich:devtools-protos2 32df92b
PiperOrigin-RevId: 339155446

java/arcs/android/devtools/DevToolsService.kt

@@ -63,6 +63,11 @@ open class DevToolsService : Service() {
   private var refModeStoreCallbackToken: Int = -1
   private var directStoreCallbackToken: Int = -1
 
+  private val initProto = DevtoolsMessage.DevToolsInitProto.newBuilder()
+    .setDevToolsVersion(0)
+    .setPlatform(DevtoolsMessage.DevToolsInitProto.Platform.ANDROID)
+    .build()
+
   override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
     // Connect to the storage service and obtain the devToolsProxy.
     scope.launch {
@@ -112,6 +117,7 @@ open class DevToolsService : Service() {
 
       binder.send(service.storageKeys ?: "")
       devToolsServer.addOnOpenWebsocketCallback {
+        devToolsServer.send(initProto.toString())
         devToolsServer.send(service.storageKeys ?: "")
       }
 

java/arcs/android/devtools/devtools_message.proto

@@ -16,3 +16,13 @@ message DevToolsProxyMessageProto {
   string storage_key = 2;
   StoreType store_type = 3;
 }
+
+message DevToolsInitProto {
+  int32 dev_tools_version = 1;
+  enum Platform {
+    PLATFORM_UNKNOWN = 0;
+    ANDROID = 1;
+    // Future types include web.
+  }
+  Platform platform = 2;
+}