Add path open errors from the permission broker to the device log.

chromeos/dbus/fake_permission_broker_client.cc

Index: chromeos/dbus/fake_permission_broker_client.cc
diff --git a/chromeos/dbus/fake_permission_broker_client.cc b/chromeos/dbus/fake_permission_broker_client.cc
index 548173b5f1b33910ec30405e510d2309549d8a2b..b1c3d6ae1522beae4833f6a90723956b5f508cfd 100644
--- a/chromeos/dbus/fake_permission_broker_client.cc
+++ b/chromeos/dbus/fake_permission_broker_client.cc
@@ -12,6 +12,7 @@
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/posix/eintr_wrapper.h"
+#include "base/strings/stringprintf.h"
 #include "base/thread_task_runner_handle.h"
 #include "base/threading/worker_pool.h"
 #include "dbus/file_descriptor.h"
@@ -27,17 +28,24 @@ namespace {
 void OpenPathAndValidate(
     const std::string& path,
     const PermissionBrokerClient::OpenPathCallback& callback,
+    const PermissionBrokerClient::ErrorCallback& error_callback,
     scoped_refptr<base::TaskRunner> task_runner) {
-  dbus::FileDescriptor dbus_fd;
   int fd = HANDLE_EINTR(open(path.c_str(), O_RDWR));
   if (fd < 0) {
-    PLOG(WARNING) << "Failed to open '" << path << "'";
+    int error_code = logging::GetLastSystemErrorCode();
+    task_runner->PostTask(
+        FROM_HERE,
+        base::Bind(error_callback, "open_failed",

[stevenjb, 2016/02/09 23:16:51]

nit: define 'open_failed' as a const, make available in header

[Reilly Grant (use Gerrit), 2016/02/09 23:54:03]

Which header do you recommend? permission_broker_client.h or
service_constants.h? Ideally these errors would be part of the interface exposed
by the permission broker service.

[stevenjb, 2016/02/10 00:01:01]

Oh, I didn't notice this was the fake. In that case feel free to ignore this,
otherwise we should use the same const that the real implementation uses if
available, or define that as a const in this file.

[Reilly Grant (use Gerrit), 2016/02/10 00:16:32]

Done.

+                   base::StringPrintf(
+                       "Failed to open '%s': %s", path.c_str(),
+                       logging::SystemErrorCodeToString(error_code).c_str())));

[stevenjb, 2016/02/09 23:16:51]

nit: return here, remove else

[Reilly Grant (use Gerrit), 2016/02/10 00:16:32]

Done.

   } else {
+    dbus::FileDescriptor dbus_fd;
     dbus_fd.PutValue(fd);
     dbus_fd.CheckValidity();
+    task_runner->PostTask(FROM_HERE,
+                          base::Bind(callback, base::Passed(&dbus_fd)));
   }
-  task_runner->PostTask(FROM_HERE,
-                        base::Bind(callback, base::Passed(&dbus_fd)));
 }
 
 }  // namespace
@@ -55,11 +63,13 @@ void FakePermissionBrokerClient::CheckPathAccess(
 }
 
 void FakePermissionBrokerClient::OpenPath(const std::string& path,
-                                          const OpenPathCallback& callback) {
-  base::WorkerPool::PostTask(FROM_HERE,
-                             base::Bind(&OpenPathAndValidate, path, callback,
-                                        base::ThreadTaskRunnerHandle::Get()),
-                             false);
+                                          const OpenPathCallback& callback,
+                                          const ErrorCallback& error_callback) {
+  base::WorkerPool::PostTask(
+      FROM_HERE,
+      base::Bind(&OpenPathAndValidate, path, callback, error_callback,
+                 base::ThreadTaskRunnerHandle::Get()),
+      false);
 }
 
 void FakePermissionBrokerClient::RequestTcpPortAccess(