Fix missing copyrights in src/dawn.

This CL adds the two missing copyright headers to files under src/dawn
and enables the lint flag by default.

Bug: dawn:1339
Change-Id: I3c3ec47b7f93dabadd0934fb93042f695e7e96fc
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/86360
Reviewed-by: Ben Clayton <bclayton@google.com>
Auto-Submit: Dan Sinclair <dsinclair@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

src/dawn/CPPLINT.cfg

@@ -1,7 +1,6 @@
 filter=-build/include_order
 filter=-build/include_what_you_use
 filter=-build/namespaces
-filter=-legal/copyright
 filter=-readability/casting
 filter=-readability/inheritance
 filter=-readability/namespace

src/dawn/native/AsyncTask.cpp

@@ -1,3 +1,17 @@
+// Copyright 2022 The Dawn Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
 #include "dawn/native/AsyncTask.h"
 
 #include "dawn/platform/DawnPlatform.h"

src/dawn/native/vulkan/ExternalHandle.h

@@ -1,3 +1,17 @@
+// Copyright 2022 The Dawn Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
 #ifndef SRC_DAWN_NATIVE_VULKAN_EXTERNALHANDLE_H_
 #define SRC_DAWN_NATIVE_VULKAN_EXTERNALHANDLE_H_