Simplify FakeGpuProcess* video accelerator tests

ui/ozone/public/ozone_gpu_test_helper.cc

Index: ui/ozone/public/ozone_gpu_test_helper.cc
diff --git a/ui/ozone/public/ozone_gpu_test_helper.cc b/ui/ozone/public/ozone_gpu_test_helper.cc
index 1fa265c6b35fd822c457ad43a5ee9dc4687b25f9..71a2fab454967a02a23be911c287ee735ce85718 100644
--- a/ui/ozone/public/ozone_gpu_test_helper.cc
+++ b/ui/ozone/public/ozone_gpu_test_helper.cc
@@ -4,6 +4,7 @@
 
 #include "ui/ozone/public/ozone_gpu_test_helper.h"
 
+#include "base/synchronization/waitable_event.h"
 #include "base/thread_task_runner_handle.h"
 #include "ipc/ipc_listener.h"
 #include "ipc/ipc_message.h"
@@ -66,7 +67,13 @@ class FakeGpuProcessHost {
   FakeGpuProcessHost(
       const scoped_refptr<base::SingleThreadTaskRunner>& gpu_task_runner)
       : gpu_task_runner_(gpu_task_runner), weak_factory_(this) {}
-  ~FakeGpuProcessHost() {}
+  ~FakeGpuProcessHost() {
+    base::WaitableEvent done(false, false);
+    gpu_task_runner_->PostTask(FROM_HERE,
+                               base::Bind(&FakeGpuProcessHost::Destroy,
+                                          weak_factory_.GetWeakPtr(), &done));
+    done.Wait();
+  }
 
   void Init() {
     base::Callback<void(IPC::Message*)> sender =
@@ -79,6 +86,12 @@ class FakeGpuProcessHost {
   }
 
  private:
+  void Destroy(base::WaitableEvent* done) {
+    DCHECK(gpu_task_runner_->BelongsToCurrentThread());
+    this->weak_factory_.InvalidateWeakPtrs();
+    done->Signal();
+  }
+
   void DispatchToGpuPlatformSupportTask(IPC::Message* msg) {
     ui::OzonePlatform::GetInstance()
         ->GetGpuPlatformSupport()