service worker: Prepare clear site data test for UI thread core.

The thread ServiceWorkerContextCore lives on (the "core thread")
will move from the IO thread to the UI thread.

This CL enables ClearSiteDataHandlerBrowserTest.StorageServiceWorkersIntegrationTest
to pass when ServiceWorkerOnUI is enabled.

Bug: 824858
Change-Id: Icde4c1b6dea04e66a4fe282c80ea74cf824e53e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1763275Reviewed-by: Christian Dullweber <dullweber@chromium.org>
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688915}

content/browser/browsing_data/clear_site_data_handler_browsertest.cc

@@ -262,8 +262,8 @@ class ClearSiteDataHandlerBrowserTest : public ContentBrowserTest {
     blink::mojom::ServiceWorkerRegistrationOptions options(
         scope_url, blink::mojom::ScriptType::kClassic,
         blink::mojom::ServiceWorkerUpdateViaCache::kImports);
-    base::PostTask(
-        FROM_HERE, {BrowserThread::IO},
+    RunOrPostTaskOnThread(
+        FROM_HERE, ServiceWorkerContextWrapper::GetCoreThreadId(),
         base::BindOnce(
             &ServiceWorkerContextWrapper::RegisterServiceWorker,
             base::Unretained(service_worker_context), js_url, options,
@@ -273,8 +273,8 @@ class ClearSiteDataHandlerBrowserTest : public ContentBrowserTest {
 
     // Wait for its activation.
     base::RunLoop run_loop;
-    base::PostTask(
-        FROM_HERE, {BrowserThread::IO},
+    RunOrPostTaskOnThread(
+        FROM_HERE, ServiceWorkerContextWrapper::GetCoreThreadId(),
         base::BindOnce(&ServiceWorkerActivationObserver::SignalActivation,
                        base::Unretained(service_worker_context),
                        run_loop.QuitClosure()));
@@ -292,8 +292,8 @@ class ClearSiteDataHandlerBrowserTest : public ContentBrowserTest {
     std::vector<StorageUsageInfo> service_workers;
     base::RunLoop run_loop;
 
-    base::PostTask(
-        FROM_HERE, {BrowserThread::IO},
+    RunOrPostTaskOnThread(
+        FROM_HERE, ServiceWorkerContextWrapper::GetCoreThreadId(),
         base::BindOnce(
             &ServiceWorkerContextWrapper::GetAllOriginsInfo,
             base::Unretained(service_worker_context),