Mark flatennable macros as block beginning/ending in .clang-format

Change-Id: I08e907cd5051d9f8cd97cdd773f9ff326cc6a0d8
Reviewed-on: https://skia-review.googlesource.com/6739
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/.clang-format b/.clang-format
index ff81590..90eedd8 100644
--- a/.clang-format
+++ b/.clang-format
@@ -70,8 +70,8 @@
 JavaScriptQuotes: Leave
 JavaScriptWrapImports: true
 KeepEmptyLinesAtTheStartOfBlocks: false
-MacroBlockBegin: ''
-MacroBlockEnd:   ''
+MacroBlockBegin: 'SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START'
+MacroBlockEnd:   'SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END'
 MaxEmptyLinesToKeep: 1
 NamespaceIndentation: None
 ObjCBlockIndentWidth: 2