base: Deprecate base::SharedMemory and base::SharedMemoryHandle

This CL deprecates base::SharedMemory(|Handle) in favor of
{Writable,ReadOnly}SharedMemoryRegion.

Deprecation comments and a presumbit warning are added.

Bug: 795291
Change-Id: Ib861e88937df93b3c3477da6a17d5689da0b0d76
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1543639
Auto-Submit: Alex Ilin <alexilin@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#645446}

PRESUBMIT.py

@@ -581,6 +581,15 @@ _BANNED_CPP_FUNCTIONS = (
       False,
       (),
     ),
+    (
+      r'base::SharedMemory(|Handle)',
+      (
+          'base::SharedMemory is deprecated. Please use',
+          '{Writable,ReadOnly}SharedMemoryRegion instead.',
+      ),
+      False,
+      (),
+    ),
     (
       r'RunMessageLoop',
       (

base/memory/shared_memory.h

@@ -65,6 +65,9 @@ struct BASE_EXPORT SharedMemoryCreateOptions {
 // SharedMemory consumes a SharedMemoryHandle [potentially one that it created]
 // to map a shared memory OS resource into the virtual address space of the
 // current process.
+//
+// DEPRECATED - Use {Writable,ReadOnly}SharedMemoryRegion instead.
+// http://crbug.com/795291
 class BASE_EXPORT SharedMemory {
  public:
   SharedMemory();

base/memory/shared_memory_handle.h

@@ -33,6 +33,9 @@ namespace base {
 // address space of the current process.
 // TODO(erikchen): This class should have strong ownership semantics to prevent
 // leaks of the underlying OS resource. https://crbug.com/640840.
+//
+// DEPRECATED - Use {Writable,ReadOnly}SharedMemoryRegion instead.
+// http://crbug.com/795291
 class BASE_EXPORT SharedMemoryHandle {
  public:
   // The default constructor returns an invalid SharedMemoryHandle.