Fix header guards in ppapi/ [1/2]

Generated mechanically as follows:

git ls-files '*.h' | grep -E '^ppapi/' |\
grep -v third_party | grep -v ppapi/lib/gl |\
grep -v ppapi/generators/ |\
parallel --xargs cpplint.py --filter=-,+build/header_guard -- 2>&1 |\
grep build/header | head -68 |\
tools/apply_cpplint_header_guard.py

Bug: 1200694
Change-Id: I696ec66ca656c70950c6e78f03d8a542dd9734a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3026804
Reviewed-by: Henrique Ferreiro <hferreiro@igalia.com>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Sumaid <ssyed@igalia.com>
Cr-Commit-Position: refs/heads/master@{#906599}

diff --git a/ppapi/proxy/plugin_resource_var.h b/ppapi/proxy/plugin_resource_var.h
index 2f7d0858..863c23b 100644
--- a/ppapi/proxy/plugin_resource_var.h
+++ b/ppapi/proxy/plugin_resource_var.h

@@ -38,4 +38,4 @@
   DISALLOW_COPY_AND_ASSIGN(PluginResourceVar);
 };
 
-#endif
+#endif  // PPAPI_PROXY_PLUGIN_RESOURCE_VAR_H_