Make header files idempotent; script to check

Change-Id: I960ded854e6bc7cdee029a7393cac2a686c41754
Reviewed-on: https://skia-review.googlesource.com/8308
Commit-Queue: Hal Canary <halcanary@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
diff --git a/src/core/SkRecordedDrawable.h b/src/core/SkRecordedDrawable.h
index de1fca5..c7ba741 100644
--- a/src/core/SkRecordedDrawable.h
+++ b/src/core/SkRecordedDrawable.h
@@ -4,6 +4,8 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
+#ifndef SkRecordedDrawable_DEFINED
+#define SkRecordedDrawable_DEFINED
 
 #include "SkBBoxHierarchy.h"
 #include "SkDrawable.h"
@@ -39,3 +41,4 @@
     std::unique_ptr<SkDrawableList> fDrawableList;
     const SkRect                    fBounds;
 };
+#endif  // SkRecordedDrawable_DEFINED