base: Fix/add header #ifndef guards.

Header guards should be defined based on the path and file name of the
header file. Some headers have it wrong, some are missing the guards,
and some just have the matching comment wrong.

R=Nico
BUG=464816

Committed: https://crrev.com/301b392761fd8f66f3a701ab1dd011c6e7a55e19
Cr-Commit-Position: refs/heads/master@{#319722}

Review URL: https://codereview.chromium.org/985003004

Cr-Commit-Position: refs/heads/master@{#319793}
diff --git a/base/sequenced_task_runner.h b/base/sequenced_task_runner.h
index 71dcf05c..6bb3f2b 100644
--- a/base/sequenced_task_runner.h
+++ b/base/sequenced_task_runner.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef BASE_SEQUENCED_TASKRUNNER_H_
-#define BASE_SEQUENCED_TASKRUNNER_H_
+#ifndef BASE_SEQUENCED_TASK_RUNNER_H_
+#define BASE_SEQUENCED_TASK_RUNNER_H_
 
 #include "base/base_export.h"
 #include "base/sequenced_task_runner_helpers.h"
@@ -156,4 +156,4 @@
 
 }  // namespace base
 
-#endif  // BASE_SEQUENCED_TASKRUNNER_H_
+#endif  // BASE_SEQUENCED_TASK_RUNNER_H_