Add a method BrokerDuplicateSharedMemoryHandle() to the sandbox.

content/common/sandbox_init_mac.cc

Index: content/common/sandbox_init_mac.cc
diff --git a/content/common/sandbox_init_mac.cc b/content/common/sandbox_init_mac.cc
index 609517932c2fe6c9e6fc8ad3430e3c550dc8f206..7e6387c10e5b8fecf5467cc72825f64953e38644 100644
--- a/content/common/sandbox_init_mac.cc
+++ b/content/common/sandbox_init_mac.cc
@@ -74,6 +74,14 @@ bool InitializeSandbox() {
   return InitializeSandbox(sandbox_type, allowed_dir);
 }
 
+bool BrokerDuplicateSharedMemoryHandle(
+    base::SharedMemoryHandle source_handle,
+    base::ProcessId target_process_id,
+    base::SharedMemoryHandle* target_handle) {
+  *target_handle = base::SharedMemory::DeepCopyHandle(source_handle, true);
+  return base::SharedMemory::IsHandleValid(*target_handle);
+}
+
 extern const char kBootstrapPortNameForNPAPIPlugins[] =
     "org.chromium.sandbox.real_bootstrap_server";