Dup command-buffer SHM handle before auto-closing.

ppapi/proxy/ppb_context_3d_proxy.cc

Index: ppapi/proxy/ppb_context_3d_proxy.cc
diff --git a/ppapi/proxy/ppb_context_3d_proxy.cc b/ppapi/proxy/ppb_context_3d_proxy.cc
index 9c1e3835675147f9b62e2886740aa5bfcefd2dd3..076f13310493f7b9076dc9c2f203a4fe00ed9dd9 100644
--- a/ppapi/proxy/ppb_context_3d_proxy.cc
+++ b/ppapi/proxy/ppb_context_3d_proxy.cc
@@ -133,8 +133,11 @@ const PPB_Context3D_Dev context_3d_interface = {
 
 base::SharedMemoryHandle SHMHandleFromInt(int shm_handle) {
 #if defined(OS_POSIX)
-  return base::FileDescriptor(shm_handle, true);
+  // The handle isn't ours to close, but we want to keep a reference to the
+  // handle until it is actually sent, so duplicate it, and mark auto-close.
+  return base::FileDescriptor(dup(shm_handle), true);
 #elif defined(OS_WIN)
+  // TODO(piman): DuplicateHandle to the plugin process.
   return reinterpret_cast<HANDLE>(shm_handle);
 #else
 #error "Platform not supported."