Mac: Require child AllocateGpuMemoryBuffer to not fail

content/child/child_io_surface_manager_mac.h

Index: content/child/child_io_surface_manager_mac.h
diff --git a/content/child/child_io_surface_manager_mac.h b/content/child/child_io_surface_manager_mac.h
index 6c849fb2541602d882f64b982c226f048e7d9e91..6110369040eebff43bccf4e848c09ab117f671d7 100644
--- a/content/child/child_io_surface_manager_mac.h
+++ b/content/child/child_io_surface_manager_mac.h
@@ -27,6 +27,8 @@ class CONTENT_EXPORT ChildIOSurfaceManager : public gfx::IOSurfaceManager {
                          IOSurfaceRef io_surface) override;
   void UnregisterIOSurface(gfx::IOSurfaceId io_surface_id,
                            int client_id) override;
+
+  // This will always return a valid IOSurface (failure will crash).

[reveman, 2015/12/01 20:49:04]

We need to be able to use this in the GPU process without crashing on failure to
solve the problem where GMBs can be become invalid after a gpu process crash.

Is it enough for now to add CHECKs to the user of this interface? If we need
CHECKs here too then let's make it clear that they are only to temporarily
diagnose some crashes by adding TODOs and keeping as much of the existing code
as is.

   IOSurfaceRef AcquireIOSurface(gfx::IOSurfaceId io_surface_id) override;
 
   // Set the service Mach port. Ownership of |service_port| is passed to the