tools/format: Format .gn files too

Change-Id: I2ff7e099e4b8a4a71e1900fdd3f904630cb87a4d
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/118501
Auto-Submit: Ben Clayton <bclayton@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>

tools/format

@@ -23,19 +23,32 @@ if ! command -v clang_format.py &> /dev/null; then
     exit 1
 fi
 
-FILES=""
-FILES+="`find src -name "*.h"` "
-FILES+="`find src -name "*.cc"` "
-FILES+="`find src -name "*.cpp"` "
-FILES+="`find src -name "*.m"` "
-FILES+="`find src -name "*.mm"` "
-FILES+="`find include -name "*.h"` "
+if ! command -v gn &> /dev/null; then
+    echo "gn not found on PATH"
+    exit 1
+fi
+
+CLANG_FORMAT_FILES=""
+CLANG_FORMAT_FILES+="`find src -name "*.h"` "
+CLANG_FORMAT_FILES+="`find src -name "*.cc"` "
+CLANG_FORMAT_FILES+="`find src -name "*.cpp"` "
+CLANG_FORMAT_FILES+="`find src -name "*.m"` "
+CLANG_FORMAT_FILES+="`find src -name "*.mm"` "
+CLANG_FORMAT_FILES+="`find include -name "*.h"` "
+
+GN_FILES="BUILD.gn "
+GN_FILES+="`find src -name "*.gn"` "
 
 if command -v go &> /dev/null; then
-    # Go is installed. Run cpplint in parallel for speed wins
+    # Go is installed. Run in parallel for speed wins
     ${SCRIPT_DIR}/run run-parallel  \
          clang_format.py -i         \
-         $ -- $FILES
+         $ -- $CLANG_FORMAT_FILES
+
+    ${SCRIPT_DIR}/run run-parallel  \
+         gn format                  \
+         $ -- $GN_FILES
 else
-    clang_format.py -i $FILES
+    clang_format.py -i $CLANG_FORMAT_FILES
+    gn format $GN_FILES
 fi