Add some missing header include guards

BUG=skia:
R=reed@google.com, bsalomon@google.com, tfarina@chromium.org

Author: george@mozilla.com

Review URL: https://codereview.chromium.org/325843002
diff --git a/src/gpu/GrReducedClip.h b/src/gpu/GrReducedClip.h
index cbb0346..e3a28cc 100644
--- a/src/gpu/GrReducedClip.h
+++ b/src/gpu/GrReducedClip.h
@@ -6,6 +6,9 @@
  * found in the LICENSE file.
  */
 
+#ifndef GrReducedClip_DEFINED
+#define GrReducedClip_DEFINED
+
 #include "SkClipStack.h"
 #include "SkTLList.h"
 
@@ -41,3 +44,5 @@
                             bool* requiresAA = NULL);
 
 } // namespace GrReducedClip
+
+#endif