Replace base::SharedMemory read-only methods with GetReadOnlyHandle.

base/memory/shared_memory_win.cc

 // Copyright (c) 2011 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 "base/memory/shared_memory.h"
 
 #include <aclapi.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 320 matching lines @@
 
 bool SharedMemory::Unmap() {
   if (memory_ == NULL)
     return false;
 
   UnmapViewOfFile(memory_);
   memory_ = NULL;
   return true;
 }
 
+SharedMemoryHandle SharedMemory::GetReadOnlyHandle() {
+  HANDLE result;
+  ProcessHandle process = GetCurrentProcess();
+  if (!::DuplicateHandle(process, mapped_file_.Get(), process, &result,
+                         FILE_MAP_READ | SECTION_QUERY, FALSE, 0)) {
+    return SharedMemoryHandle();
+  }
+  SharedMemoryHandle handle =
+      SharedMemoryHandle(result, base::GetProcId(process));
+  handle.SetOwnershipPassesToIPC(true);

[Jeffrey Yasskin, 2017/05/01 22:16:34]

Does this need to show up in the interface of GetReadOnlyHandle()? It looks like
it's only valid to use the resulting handle once?

[erikchen, 2017/05/02 01:53:08]

Done.

+  return handle;
+}
+
 bool SharedMemory::ShareToProcessCommon(ProcessHandle process,
                                         SharedMemoryHandle* new_handle,
-                                        bool close_self,
-                                        ShareMode share_mode) {
+                                        bool close_self) {
   *new_handle = SharedMemoryHandle();
   DWORD access = FILE_MAP_READ | SECTION_QUERY;
   DWORD options = 0;
   HANDLE mapped_file = mapped_file_.Get();
   HANDLE result;
-  if (share_mode == SHARE_CURRENT_MODE && !read_only_)
+  if (!read_only_)
     access |= FILE_MAP_WRITE;
   if (close_self) {
     // DUPLICATE_CLOSE_SOURCE causes DuplicateHandle to close mapped_file.
     options = DUPLICATE_CLOSE_SOURCE;
     HANDLE detached_handle = mapped_file_.Take();
     DCHECK_EQ(detached_handle, mapped_file);
     Unmap();
   }
 
   if (process == GetCurrentProcess() && close_self) {
@@ skipping 21 matching lines @@
 
 SharedMemoryHandle SharedMemory::TakeHandle() {
   SharedMemoryHandle handle(mapped_file_.Take(), base::GetCurrentProcId());
   handle.SetOwnershipPassesToIPC(true);
   memory_ = nullptr;
   mapped_size_ = 0;
   return handle;
 }
 
 }  // namespace base