Mojo: clang-format mojo/public/c/... and add a presubmit check.

mojo/public/c/system/tests/macros_unittest.cc

Index: mojo/public/c/system/tests/macros_unittest.cc
diff --git a/mojo/public/c/system/tests/macros_unittest.cc b/mojo/public/c/system/tests/macros_unittest.cc
index fdc0c87c99c2d40a40b15f1a5681a2078cc15f81..6a694b81b1b1c6e1ee078129bf6e425fe48e759a 100644
--- a/mojo/public/c/system/tests/macros_unittest.cc
+++ b/mojo/public/c/system/tests/macros_unittest.cc
@@ -58,11 +58,17 @@ TEST(MacrosTest, Alignof) {
 #if defined(_MSC_VER)
 #pragma warning(push)
 // Disable the warning "structure was padded due to __declspec(align())".
-#pragma warning(disable:4324)
+#pragma warning(disable : 4324)
 #endif
-struct MOJO_ALIGNAS(1) StructAlignas1 { char x; };
-struct MOJO_ALIGNAS(4) StructAlignas4 { char x; };
-struct MOJO_ALIGNAS(8) StructAlignas8 { char x; };
+struct MOJO_ALIGNAS(1) StructAlignas1 {
+  char x;
+};
+struct MOJO_ALIGNAS(4) StructAlignas4 {
+  char x;
+};
+struct MOJO_ALIGNAS(8) StructAlignas8 {
+  char x;
+};
 #if defined(_MSC_VER)
 #pragma warning(pop)
 #endif