Match clang-format to Dawn version.

The formatting was updated to match dawn, but the clang-format file was
never copied back into the Tint mirror.

Sync the .clang-format files.

Bug: tint:1933
Change-Id: Icaca596a3bb0e5b6733911d9fff8e42e451489b4
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/180140
Kokoro: dan sinclair <dsinclair@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
diff --git a/.clang-format b/.clang-format
index 2fb833a..d9e1846 100644
--- a/.clang-format
+++ b/.clang-format
@@ -1,2 +1,10 @@
 # http://clang.llvm.org/docs/ClangFormatStyleOptions.html
 BasedOnStyle: Chromium
+
+ColumnLimit: 100
+
+# Use 4 space indents
+IndentWidth: 4
+ObjCBlockIndentWidth: 4
+AccessModifierOffset: -2
+InsertBraces: true
\ No newline at end of file