run clang-tidy on headers too

Without -header-filter='.*' clang-tidy only checks the .cpp file.

Change-Id: Ib49081faa2ddf20222dfeb15841cf2b812c22462
Reviewed-on: https://skia-review.googlesource.com/c/176967
Commit-Queue: Mike Klein <mtklein@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/tools/clang-tidy.sh b/tools/clang-tidy.sh
index 08b041a..addbee3 100755
--- a/tools/clang-tidy.sh
+++ b/tools/clang-tidy.sh
@@ -24,7 +24,7 @@
 done
 
 if [ "$src" ]; then
-    clang-tidy -quiet -warnings-as-errors='*' $src -- $args
+    clang-tidy -quiet -header-filter='.*' -warnings-as-errors='*' $src -- $args
 fi
 exec clang++ $args