content: Add overdraw feedback support for X11 ChromeOS builds.

content/browser/compositor/gpu_browser_compositor_output_surface.cc

Index: content/browser/compositor/gpu_browser_compositor_output_surface.cc
diff --git a/content/browser/compositor/gpu_browser_compositor_output_surface.cc b/content/browser/compositor/gpu_browser_compositor_output_surface.cc
index 995b7a446d822780d285c14cb5703963b06fa7f4..30641409bebb2ec7a66a841a8473bfed3eeb2ae7 100644
--- a/content/browser/compositor/gpu_browser_compositor_output_surface.cc
+++ b/content/browser/compositor/gpu_browser_compositor_output_surface.cc
@@ -24,7 +24,8 @@ GpuBrowserCompositorOutputSurface::GpuBrowserCompositorOutputSurface(
     scoped_refptr<ui::ContextProviderCommandBuffer> context,
     const UpdateVSyncParametersCallback& update_vsync_parameters_callback,
     std::unique_ptr<display_compositor::CompositorOverlayCandidateValidator>
-        overlay_candidate_validator)
+        overlay_candidate_validator,
+    bool support_stencil)
     : BrowserCompositorOutputSurface(std::move(context),
                                      update_vsync_parameters_callback,
                                      std::move(overlay_candidate_validator)),
@@ -33,6 +34,7 @@ GpuBrowserCompositorOutputSurface::GpuBrowserCompositorOutputSurface(
     capabilities_.flipped_output_surface =
         context_provider()->ContextCapabilities().flips_vertically;
   }
+  capabilities_.supports_stencil = support_stencil;

[jbauman, 2017/01/19 01:53:59]

We should really try to grab this from the context, as there's no guarantee it's
supported even if we ask for it.

[reveman, 2017/01/19 04:15:08]

I think what we really want to do is prefer an X visual with stencil bits and
only mark this as supported if one was found. That is if we're on X11 (only case
today when this will be true and we're not surfaceless). It happens that the
preferred visual on X always has stencil support and I considered adding some
code here to check that but it seemed overkill for this debugging feature. Added
a TODO here to latest patch that we can follow up on if needed.

 }
 
 GpuBrowserCompositorOutputSurface::~GpuBrowserCompositorOutputSurface() {