Revert of base: Make shared memory backed by Mach primitives by default.

base/memory/shared_memory_mac.cc

Index: base/memory/shared_memory_mac.cc
diff --git a/base/memory/shared_memory_mac.cc b/base/memory/shared_memory_mac.cc
index cdf0bc9fefa4eb60fd4333abdfd66c64b1009b89..61ebf89aa1540c8f646af5b79b31618b124432a3 100644
--- a/base/memory/shared_memory_mac.cc
+++ b/base/memory/shared_memory_mac.cc
@@ -53,7 +53,7 @@
     group = SharedMemoryHandle::POSIX;
     found_group = true;
   } else {
-    group = SharedMemoryHandle::MACH;
+    group = SharedMemoryHandle::POSIX;
   }
 
   return group;
@@ -175,20 +175,10 @@
 }  // namespace
 
 SharedMemoryCreateOptions::SharedMemoryCreateOptions()
-    : type(SharedMemoryHandle::MACH),
+    : type(SharedMemoryHandle::POSIX),
       size(0),
       executable(false),
-      share_read_only(false) {
-  if (mac::IsOSLionOrLater()) {
-    // A/B test the mechanism. Once the experiment is over, this will always be
-    // set to SharedMemoryHandle::MACH.
-    // http://crbug.com/547261
-    type = GetABTestMechanism();
-  } else {
-    // Mach shared memory isn't supported on OSX 10.6 or older.
-    type = SharedMemoryHandle::POSIX;
-  }
-}
+      share_read_only(false) {}
 
 SharedMemory::SharedMemory()
     : mapped_memory_mechanism_(SharedMemoryHandle::POSIX),
@@ -273,6 +263,22 @@
   return Create(options);
 }
 
+bool SharedMemory::CreateAndMapAnonymousMach(size_t size) {
+  SharedMemoryCreateOptions options;
+
+  if (mac::IsOSLionOrLater()) {
+    // A/B test the mechanism. Once the experiment is over, this will always be
+    // set to SharedMemoryHandle::MACH.
+    // http://crbug.com/547261
+    options.type = GetABTestMechanism();
+  } else {
+    // Mach shared memory isn't supported on OSX 10.6 or older.
+    options.type = SharedMemoryHandle::POSIX;
+  }
+  options.size = size;
+  return Create(options) && Map(size);
+}
+
 // static
 bool SharedMemory::GetSizeFromSharedMemoryHandle(
     const SharedMemoryHandle& handle,