Add HidConnection::Close and register OS X callbacks on the UI thread.

The platform implementation of a HID connection may need to cancel I/O
operations when the connection is closed. If this is done during the
object destructor then any pointers held by those pending operations are
immediately invalid. A separate Close method allows the cleanup to
happen while the object is still available to handle asynchronous
cancellation events.

The OS X implementation will take advantage of this immediately to
register and unregister its input report callback from the UI thread to
avoid a race between event delivery and object cleanup. I've added
comments explaining why not all operations on the IOHIDDevice object
could be moved to the UI thread.

BUG=418207

Review URL: https://codereview.chromium.org/615633008

Cr-Commit-Position: refs/heads/master@{#298384}

1 files changed, 10 insertions, 1 deletions

diff --git a/device/hid/hid_connection.cc b/device/hid/hid_connection.cc
index 5df2a01..5ff39f3 100644
--- a/device/hid/hid_connection.cc
+++ b/device/hid/hid_connection.cc
@@ -64,12 +64,21 @@ bool HasProtectedCollection(const HidDeviceInfo& device_info) {
 }  // namespace
 
 HidConnection::HidConnection(const HidDeviceInfo& device_info)
-    : device_info_(device_info) {
+    : device_info_(device_info), closed_(false) {
   has_protected_collection_ = HasProtectedCollection(device_info);
 }
 
 HidConnection::~HidConnection() {
   DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(closed_);
+}
+
+void HidConnection::Close() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(!closed_);
+
+  PlatformClose();
+  closed_ = true;
 }
 
 void HidConnection::Read(const ReadCallback& callback) {