ozone: demo: Defer renderer creation until nonzero size

Fuchsia platform windows are initially 0x0 and this causes vulkan surface
creation to crash. Defer creating a renderer until we have a nonempty
size.

Bug: 861853
Test: run_ozone_demo --ozone-platform=scenic --enable-vulkan

Change-Id: I74e14ed07ab47ebc22730b40cf36217e9ae4873a
Reviewed-on: https://chromium-review.googlesource.com/1229162
Commit-Queue: Michael Spang <spang@chromium.org>
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592110}

ui/ozone/demo/demo_window.cc

@@ -66,16 +66,16 @@ gfx::Size DemoWindow::GetSize() {
 }
 
 void DemoWindow::Start() {
-  base::ThreadTaskRunnerHandle::Get()->PostTask(
-      FROM_HERE,
-      base::BindOnce(&DemoWindow::StartOnGpu, weak_ptr_factory_.GetWeakPtr()));
+  StartRendererIfNecessary();
 }
 
 void DemoWindow::Quit() {
   window_manager_->Quit();
 }
 
-void DemoWindow::OnBoundsChanged(const gfx::Rect& new_bounds) {}
+void DemoWindow::OnBoundsChanged(const gfx::Rect& new_bounds) {
+  StartRendererIfNecessary();
+}
 
 void DemoWindow::OnDamageRect(const gfx::Rect& damaged_region) {}
 
@@ -105,7 +105,9 @@ void DemoWindow::OnAcceleratedWidgetDestroyed() {
 
 void DemoWindow::OnActivationChanged(bool active) {}
 
-void DemoWindow::StartOnGpu() {
+void DemoWindow::StartRendererIfNecessary() {
+  if (renderer_ || GetSize().IsEmpty())
+    return;
   renderer_ =
       renderer_factory_->CreateRenderer(GetAcceleratedWidget(), GetSize());
   if (!renderer_->Initialize())

ui/ozone/demo/demo_window.h

@@ -47,7 +47,7 @@ class DemoWindow : public PlatformWindowDelegate {
  private:
   // Since we pretend to have a GPU process, we should also pretend to
   // initialize the GPU resources via a posted task.
-  void StartOnGpu();
+  void StartRendererIfNecessary();
 
   WindowManager* window_manager_;      // Not owned.
   RendererFactory* renderer_factory_;  // Not owned.