Windows: Fix an invalid handle when printing.

components/printing/renderer/print_web_view_helper_pdf_win.cc

Index: components/printing/renderer/print_web_view_helper_pdf_win.cc
diff --git a/components/printing/renderer/print_web_view_helper_pdf_win.cc b/components/printing/renderer/print_web_view_helper_pdf_win.cc
index c8ea15ca5ce987d51e29a29f7a23d3f52778a9d8..2bf616a9ef3481af0010ddbb20c1df0b920d01d4 100644
--- a/components/printing/renderer/print_web_view_helper_pdf_win.cc
+++ b/components/printing/renderer/print_web_view_helper_pdf_win.cc
@@ -60,10 +60,8 @@ bool PrintWebViewHelper::PrintPagesNative(blink::WebLocalFrame* frame,
     printed_page_params.content_area = content_area_in_dpi[i];
     Send(new PrintHostMsg_DidPrintPage(routing_id(), printed_page_params));
     // Send the rest of the pages with an invalid metafile handle.
-    if (printed_page_params.metafile_data_handle.IsValid()) {
-      printed_page_params.metafile_data_handle.Close();
+    if (printed_page_params.metafile_data_handle.IsValid())

[erikchen, 2016/08/25 01:20:00]

This works, but probably not the way we wanted it to. :(

https://cs.chromium.org/chromium/src/base/memory/shared_memory_handle_win.cc?...

SharedMemoryHandle::Close() is a const method that calls CloseHandle() on the
underlying handle_. But it doesn't touch handle_. 

SharedMemoryHandle::IsValid just checks if handle_ is nullptr.

[If we assume sane semantics for Close() and IsValid(), then the existing
implementation is nonsense. That's also why the crash existed to begin with -
why would it not be valid to Close a Valid handle?]

I bet that all of these weird semantics stem from base::FileDescriptor. Could
you add:

// TODO(erikchen): Fix semantics. See https://crbug.com/640840

[Lei Zhang, 2016/08/25 16:42:03]

Done.

       printed_page_params.metafile_data_handle = base::SharedMemoryHandle();
-    }
   }
   return true;
 }