make base::SharedMemoryHandle a class on POSIX.

components/printing/renderer/print_web_view_helper_linux.cc

Index: components/printing/renderer/print_web_view_helper_linux.cc
diff --git a/components/printing/renderer/print_web_view_helper_linux.cc b/components/printing/renderer/print_web_view_helper_linux.cc
index dac616a6bb6cabe1ca289af705c45f4789d0f31a..5ac54c11ba1afda4b80132c8bfb6297588eb7884 100644
--- a/components/printing/renderer/print_web_view_helper_linux.cc
+++ b/components/printing/renderer/print_web_view_helper_linux.cc
@@ -94,7 +94,7 @@ bool PrintWebViewHelper::PrintPagesNative(blink::WebLocalFrame* frame,
     printed_page_params.page_number = printed_pages[i];
     Send(new PrintHostMsg_DidPrintPage(routing_id(), printed_page_params));
     // Send the rest of the pages with an invalid metafile handle.
-    printed_page_params.metafile_data_handle.fd = -1;
+    printed_page_params.metafile_data_handle.Invalidate();
   }
   return true;
 #endif  // defined(OS_ANDROID)