service worker: Prepare more clear site data tests 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 the following to pass when ServiceWorkerOnUI is enabled:
- SameSiteDataRemoverBrowserTest.TestClearDataWithStorageRemoval
- SameSiteDataRemoverBrowserTest.TestClearDataWithoutStorageRemoval

Bug: 824858
Change-Id: Iaace639ff7425d4c933d18c5662cd67024790fe4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1763351Reviewed-by: Christian Dullweber <dullweber@chromium.org>
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688922}

content/browser/browsing_data/same_site_data_remover_impl_browsertest.cc

@@ -145,8 +145,8 @@ class SameSiteDataRemoverBrowserTest : 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,
@@ -156,8 +156,8 @@ class SameSiteDataRemoverBrowserTest : 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()));
@@ -174,8 +174,8 @@ class SameSiteDataRemoverBrowserTest : 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),