Windows: Fix an invalid handle when printing.

components/printing/renderer/print_web_view_helper_pdf_win.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/printing/renderer/print_web_view_helper.h"
 
 #include <stddef.h>
 
 #include "base/logging.h"
 #include "base/process/process_handle.h"
@@ skipping 42 matching lines @@
   printed_page_params.data_size = metafile.GetDataSize();
   printed_page_params.document_cookie = params.params.document_cookie;
   printed_page_params.page_size = params.params.page_size;
 
   for (size_t i = 0; i < printed_pages.size(); ++i) {
     printed_page_params.page_number = printed_pages[i];
     printed_page_params.page_size = page_size_in_dpi[i];
     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;
 }
 #endif  // defined(ENABLE_BASIC_PRINTING)
 
 }  // namespace printing