Make sure all callbacks are executed in ServiceWorkerBrowserTest

This CL attempts to fix flakiness of some service worker browsertests.

Before this CL, we destroyed ServiceWorkerContextWrapper in
TearDownOnMainThread() without waiting for all callbacks are executed.
This caused DCHECK hit in mojo callbacks of
ServiceWorkerStorageControl because destroying the wrapper also
destroys a mojo connection to ServiceWorkerStorageControl. Mojo
callbacks need to be executed before the corresponding remote is
destroyed.

Bug: 1137529
Change-Id: I3060d5ba687e8164c6f29f1e24395ce09c26abfe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2467037Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816429}

content/browser/service_worker/service_worker_browsertest.cc

@@ -348,8 +348,10 @@ class ServiceWorkerBrowserTest : public ContentBrowserTest {
   }
 
   void TearDownOnMainThread() override {
-    RunOnCoreThread(
-        base::BindOnce(&self::TearDownOnCoreThread, base::Unretained(this)));
+    base::RunLoop loop;
+    RunOnCoreThread(base::BindOnce(&self::TearDownOnCoreThread,
+                                   base::Unretained(this), loop.QuitClosure()));
+    loop.Run();
     wrapper_ = nullptr;
   }
 
@@ -368,7 +370,16 @@ class ServiceWorkerBrowserTest : public ContentBrowserTest {
   }
 
   virtual void SetUpOnCoreThread() {}
-  virtual void TearDownOnCoreThread() {}
+
+  virtual void TearDownOnCoreThread(base::OnceClosure callback) {
+    // Flush remote storage control so that all pending callbacks are executed.
+    wrapper()
+        ->context()
+        ->registry()
+        ->GetRemoteStorageControl()
+        .FlushForTesting();
+    std::move(callback).Run();
+  }
 
   ServiceWorkerContextWrapper* wrapper() { return wrapper_.get(); }
   ServiceWorkerContext* public_context() { return wrapper(); }