Do not expose BundleDownloader from DevServerHelper

Summary:
Adds `downloadBundleFromURL` as a delegating method to `DevServerHelper` rather than exposing the underlying `BundleDownloader`.

The additional encapsulation will allow futher factoring of `BundleDownloader` to make logic for different delta bundler clients easier to implement and maintain.

Reviewed By: pakoito

Differential Revision: D6871225

fbshipit-source-id: 6adcab5e69869a234baf38f1f1e60abd34d6b555

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

@@ -19,6 +19,7 @@
 import com.facebook.react.bridge.UiThreadUtil;
 import com.facebook.react.common.ReactConstants;
 import com.facebook.react.common.network.OkHttpCallUtil;
+import com.facebook.react.devsupport.interfaces.DevBundleDownloadListener;
 import com.facebook.react.devsupport.interfaces.PackagerStatusCallback;
 import com.facebook.react.devsupport.interfaces.StackFrame;
 import com.facebook.react.modules.systeminfo.AndroidInfoHelpers;
@@ -391,8 +392,10 @@ public String getInspectorAttachUrl(String title) {
         AndroidInfoHelpers.getFriendlyDeviceName());
   }
 
-  public BundleDownloader getBundleDownloader() {
-    return mBundleDownloader;
+  public void downloadBundleFromURL(
+    DevBundleDownloadListener callback,
+    File outputFile, String bundleURL, BundleDownloader.BundleInfo bundleInfo) {
+    mBundleDownloader.downloadBundleFromURL(callback, outputFile, bundleURL, bundleInfo);
   }
 
   /**

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

@@ -1039,7 +1039,7 @@ public void reloadJSFromServer(final String bundleURL) {
 
     final BundleDownloader.BundleInfo bundleInfo = new BundleDownloader.BundleInfo();
 
-    mDevServerHelper.getBundleDownloader().downloadBundleFromURL(
+    mDevServerHelper.downloadBundleFromURL(
         new DevBundleDownloadListener() {
           @Override
           public void onSuccess() {