Fix crash in PPB_Graphics3D_Impl destructor.

content/renderer/pepper/ppb_graphics_3d_impl.cc

Index: content/renderer/pepper/ppb_graphics_3d_impl.cc
diff --git a/content/renderer/pepper/ppb_graphics_3d_impl.cc b/content/renderer/pepper/ppb_graphics_3d_impl.cc
index 691f524497ad9cc53dd90b6dff80e2ea31878c10..24c6513c12fb8119bb4d5ef6293d885dcc83d5e9 100644
--- a/content/renderer/pepper/ppb_graphics_3d_impl.cc
+++ b/content/renderer/pepper/ppb_graphics_3d_impl.cc
@@ -46,7 +46,10 @@ PPB_Graphics3D_Impl::PPB_Graphics3D_Impl(PP_Instance instance)
       weak_ptr_factory_(this) {}
 
 PPB_Graphics3D_Impl::~PPB_Graphics3D_Impl() {
-  command_buffer_->SetGpuControlClient(nullptr);
+  // Unset the client before the command_buffer_ is destroyed, similar to how
+  // WeakPtrFactory invalidates before it.
+  if (command_buffer_)
+    command_buffer_->SetGpuControlClient(nullptr);
 }
 
 // static