Enable build/header_guard

This CL enables the build/header_guard lint check. The existing headers
which failed the check were updated, missing headers added. An exclusion
file for the generator templates was added as well.

Bug: dawn:1339
Change-Id: If572e460179ad501293d5d6cf01e0ea900daa979
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/86207
Reviewed-by: Ben Clayton <bclayton@google.com>
Auto-Submit: Dan Sinclair <dsinclair@chromium.org>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>

src/dawn/tests/DawnNativeTest.h

diff --git a/src/dawn/tests/DawnNativeTest.h b/src/dawn/tests/DawnNativeTest.h
index 9e8df19..8d6fd8e 100644
--- a/src/dawn/tests/DawnNativeTest.h
+++ b/src/dawn/tests/DawnNativeTest.h
@@ -12,8 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#ifndef TESTS_DAWNNATIVETEST_H_
-#define TESTS_DAWNNATIVETEST_H_
+#ifndef SRC_DAWN_TESTS_DAWNNATIVETEST_H_
+#define SRC_DAWN_TESTS_DAWNNATIVETEST_H_
 
 #include <gtest/gtest.h>
 
@@ -50,4 +50,4 @@
     static void OnDeviceError(WGPUErrorType type, const char* message, void* userdata);
 };
 
-#endif  // TESTS_DAWNNATIVETEST_H_
+#endif  // SRC_DAWN_TESTS_DAWNNATIVETEST_H_