mus: Always use the GPU compositor for mus.

content/browser/compositor/gpu_process_transport_factory.cc

Index: content/browser/compositor/gpu_process_transport_factory.cc
diff --git a/content/browser/compositor/gpu_process_transport_factory.cc b/content/browser/compositor/gpu_process_transport_factory.cc
index c3d27592271913680f48b701b5dd2e03855e0255..e00aa43fc6fa00adefdad857c336d12022e504e4 100644
--- a/content/browser/compositor/gpu_process_transport_factory.cc
+++ b/content/browser/compositor/gpu_process_transport_factory.cc
@@ -107,6 +107,27 @@ bool IsUsingMus() {
   return shell::ShellIsRemote();
 }
 
+static bool ShouldCreateGpuOutputSurface(ui::Compositor* compositor) {
+#if defined(OS_CHROMEOS)
+  // Software fallback does not happen on Chrome OS.
+  return true;
+#endif
+
+  if (IsUsingMus()) {
+    // There will always be a GPU process.
+    return true;
+  }
+
+#if defined(OS_WIN)
+  if (compositor && ::GetProp(compositor->widget(), kForceSoftwareCompositor) &&
+      ::RemoveProp(compositor->widget(), kForceSoftwareCompositor))
+    return false;
+#endif
+
+  return content::GpuDataManagerImpl::GetInstance()
+      ->CanUseGpuBrowserCompositor();
+}
+
 scoped_refptr<content::ContextProviderCommandBuffer> CreateContextCommon(
     scoped_refptr<gpu::GpuChannelHost> gpu_channel_host,
     gpu::SurfaceHandle surface_handle,
@@ -114,8 +135,7 @@ scoped_refptr<content::ContextProviderCommandBuffer> CreateContextCommon(
     bool support_locking,
     content::ContextProviderCommandBuffer* shared_context_provider,
     content::command_buffer_metrics::ContextType type) {
-  DCHECK(
-      content::GpuDataManagerImpl::GetInstance()->CanUseGpuBrowserCompositor());
+  DCHECK(ShouldCreateGpuOutputSurface(nullptr));

[danakj, 2016/08/12 17:48:29]

This is tied to the change for shared main thread context so explanation there
should explain this.

   DCHECK(gpu_channel_host);
 
   // This is called from a few places to create different contexts:
@@ -264,21 +284,6 @@ CreateOverlayCandidateValidator(gfx::AcceleratedWidget widget) {
   return validator;
 }
 
-static bool ShouldCreateGpuOutputSurface(ui::Compositor* compositor) {
-#if defined(OS_CHROMEOS)
-  // Software fallback does not happen on Chrome OS.
-  return true;
-#endif
-
-#if defined(OS_WIN)
-  if (::GetProp(compositor->widget(), kForceSoftwareCompositor) &&
-      ::RemoveProp(compositor->widget(), kForceSoftwareCompositor))
-    return false;
-#endif
-
-  return GpuDataManagerImpl::GetInstance()->CanUseGpuBrowserCompositor();
-}
-
 void GpuProcessTransportFactory::CreateOutputSurface(
     base::WeakPtr<ui::Compositor> compositor) {
   DCHECK(!!compositor);
@@ -361,7 +366,7 @@ void GpuProcessTransportFactory::EstablishedGpuChannel(
     }
 
     scoped_refptr<gpu::GpuChannelHost> gpu_channel_host;
-    if (GpuDataManagerImpl::GetInstance()->CanUseGpuBrowserCompositor())
+    if (ShouldCreateGpuOutputSurface(nullptr))

[danakj, 2016/08/12 17:48:29]

I don't think this should change. The fact that we're here means that
ShouldCreateGpuOutputSurface was previously true already.

I think that CanUseGpuBrowserCompositor can change tho, due to gpu crashes and
stuff. But the other things in ShouldCreateGpuOutputSurface can't. So this is
checking a bunch of redundant things which obfuscates things.

Is CanUseGpuBrowserCompositor not returning true for mus? Cuz that sounds
problematic if this code does not agree with the GpuDataManager.

       gpu_channel_host = std::move(established_channel_host);
 
     if (!gpu_channel_host) {
@@ -767,7 +772,7 @@ GpuProcessTransportFactory::SharedMainThreadContextProvider() {
   if (shared_main_thread_contexts_)
     return shared_main_thread_contexts_;
 
-  if (!GpuDataManagerImpl::GetInstance()->CanUseGpuBrowserCompositor())
+  if (!ShouldCreateGpuOutputSurface(nullptr))

[danakj, 2016/08/12 17:48:29]

This might be right but it has nothing to do with the patch description, which
is using gpu on mus. I'd like to know an explanation for this being correct
either way..

     return nullptr;
 
   DCHECK(gpu_channel_factory_);