Fix `InspectorPackagerConnection` creates too many Threads when WebSo…

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- [ ] Provide a **test plan** demonstrating that the code is solid.
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InspectorPackagerConnection now creates a new OkHttpClient when previous connection fails. If the failures occur frequently, many Threads are created in `WebSocketCall.enqueue()`. On my Pixel phone, I have seen up to 260 Threads named "OkHttp ConnectionPool" alive at the same time. So, why don't we consider reusing the existing OkHttpClient instance ?

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[1]: https://medium.com/martinkonicek/what-is-a-test-plan-8bfc840ec171#.y9lcuqqi9
[2]: https://code.facebook.com/cla
[3]: https://travis-ci.org/facebook/react-native
[4]: http://circleci.com/gh/facebook/react-native
[5]: https://github.com/facebook/react-native/blob/master/CONTRIBUTING.md#pull-requests
Closes https://github.com/facebook/react-native/pull/14301

Differential Revision: D5172277

Pulled By: javache

fbshipit-source-id: 7d417fa0675eb627f0b1ca41847b75686c8d1f3e

ReactAndroid/src/main/java/com/facebook/react/devsupport/InspectorPackagerConnection.java

@@ -176,6 +176,7 @@ public class InspectorPackagerConnection {
 
     private final String mUrl;
 
+    private OkHttpClient mHttpClient;
     private @Nullable WebSocket mWebSocket;
     private final Handler mHandler;
     private boolean mClosed;
@@ -223,14 +224,16 @@ public class InspectorPackagerConnection {
       if (mClosed) {
         throw new IllegalStateException("Can't connect closed client");
       }
-      OkHttpClient httpClient = new OkHttpClient.Builder()
-          .connectTimeout(10, TimeUnit.SECONDS)
-          .writeTimeout(10, TimeUnit.SECONDS)
-          .readTimeout(0, TimeUnit.MINUTES) // Disable timeouts for read
-          .build();
+      if (mHttpClient == null) {
+        mHttpClient = new OkHttpClient.Builder()
+            .connectTimeout(10, TimeUnit.SECONDS)
+            .writeTimeout(10, TimeUnit.SECONDS)
+            .readTimeout(0, TimeUnit.MINUTES) // Disable timeouts for read
+            .build();
+      }
 
       Request request = new Request.Builder().url(mUrl).build();
-      httpClient.newWebSocket(request, this);
+      mHttpClient.newWebSocket(request, this);
     }
 
     private void reconnect() {