ServiceWorkerOnUI: Fix background sync on Android.

This fixes the tests on Android and enables it in testing, following up
on r695883.

Bug: 824858
TBR: bcwhite
Change-Id: I04ea9c9d44f7b0eea933354c44b7c8116e9f9f35
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1799645
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695922}

content/browser/android/background_sync_network_observer_android.cc

@@ -8,6 +8,7 @@
 #include "base/task/post_task.h"
 #include "content/public/android/content_jni_headers/BackgroundSyncNetworkObserver_jni.h"
 #include "content/public/browser/browser_task_traits.h"
+#include "content/public/browser/service_worker_context.h"
 
 using base::android::JavaParamRef;
 
@@ -17,11 +18,11 @@ namespace content {
 scoped_refptr<BackgroundSyncNetworkObserverAndroid::Observer>
 BackgroundSyncNetworkObserverAndroid::Observer::Create(
     base::RepeatingCallback<void(network::mojom::ConnectionType)> callback) {
-  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+  DCHECK_CURRENTLY_ON(ServiceWorkerContext::GetCoreThreadId());
   scoped_refptr<BackgroundSyncNetworkObserverAndroid::Observer> observer(
       new BackgroundSyncNetworkObserverAndroid::Observer(callback));
-  base::PostTask(
-      FROM_HERE, {BrowserThread::UI},
+  RunOrPostTaskOnThread(
+      FROM_HERE, BrowserThread::UI,
       base::BindOnce(&BackgroundSyncNetworkObserverAndroid::Observer::Init,
                      observer));
   return observer;
@@ -51,8 +52,8 @@ void BackgroundSyncNetworkObserverAndroid::Observer::
                                 const JavaParamRef<jobject>& jcaller,
                                 jint new_connection_type) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
-  base::PostTask(
-      FROM_HERE, {BrowserThread::IO},
+  RunOrPostTaskOnThread(
+      FROM_HERE, ServiceWorkerContext::GetCoreThreadId(),
       base::BindOnce(callback_, static_cast<network::mojom::ConnectionType>(
                                     new_connection_type)));
 }
@@ -60,13 +61,13 @@ void BackgroundSyncNetworkObserverAndroid::Observer::
 BackgroundSyncNetworkObserverAndroid::Observer::Observer(
     base::RepeatingCallback<void(network::mojom::ConnectionType)> callback)
     : callback_(callback) {
-  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+  DCHECK_CURRENTLY_ON(ServiceWorkerContext::GetCoreThreadId());
 }
 
 BackgroundSyncNetworkObserverAndroid::BackgroundSyncNetworkObserverAndroid(
     const base::Closure& network_changed_callback)
     : BackgroundSyncNetworkObserver(network_changed_callback) {
-  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+  DCHECK_CURRENTLY_ON(ServiceWorkerContext::GetCoreThreadId());
 
   observer_ = Observer::Create(
       base::Bind(&BackgroundSyncNetworkObserverAndroid::OnConnectionChanged,
@@ -74,7 +75,7 @@ BackgroundSyncNetworkObserverAndroid::BackgroundSyncNetworkObserverAndroid(
 }
 
 BackgroundSyncNetworkObserverAndroid::~BackgroundSyncNetworkObserverAndroid() {
-  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+  DCHECK_CURRENTLY_ON(ServiceWorkerContext::GetCoreThreadId());
 }
 
 void BackgroundSyncNetworkObserverAndroid::RegisterWithNetworkConnectionTracker(

testing/variations/fieldtrial_testing_config.json

@@ -5264,6 +5264,8 @@
     "ServiceWorkerOnUI": [
         {
             "platforms": [
+                "android",
+                "android_webview",
                 "chromeos",
                 "linux",
                 "mac",