Mojo: Require our public options structs to be aligned like int64_t's.

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 5225b67cdbf7371158f32dca80ab4678630fe3b0..4214325cd7c13f714df62dec6088831210be9db9 100644
--- a/mojo/public/c/system/tests/macros_unittest.cc
+++ b/mojo/public/c/system/tests/macros_unittest.cc
@@ -44,5 +44,28 @@ TEST(MacrosTest, CompileAssert) {
                       bad_compile_assert_failure);
 }
 
+TEST(MacrosTest, Alignof) {
+  // Strictly speaking, this isn't a portable test, but I think it'll pass on
+  // all the platforms we currently support.
+  EXPECT_EQ(1u, MOJO_ALIGNOF(char));
+  EXPECT_EQ(4u, MOJO_ALIGNOF(int32_t));
+  EXPECT_EQ(8u, MOJO_ALIGNOF(int64_t));
+  EXPECT_EQ(8u, MOJO_ALIGNOF(double));
+}
+
+// These structs are used in the Alignas test. Define them globally to avoid
+// MSVS warnings/errors.
+struct MOJO_ALIGNAS(1) StructAlignas1 { char x; };
+struct MOJO_ALIGNAS(4) StructAlignas4 { char x; };
+struct MOJO_ALIGNAS(8) StructAlignas8 { char x; };
+struct MOJO_ALIGNAS(MOJO_ALIGNOF(int64_t)) StructAlignasInt64 { char x; };
+
+TEST(MacrosTest, Alignas) {
+  EXPECT_EQ(1u, MOJO_ALIGNOF(StructAlignas1));
+  EXPECT_EQ(4u, MOJO_ALIGNOF(StructAlignas4));
+  EXPECT_EQ(8u, MOJO_ALIGNOF(StructAlignas8));
+  EXPECT_EQ(MOJO_ALIGNOF(int64_t), MOJO_ALIGNOF(StructAlignasInt64));
+}
+
 }  // namespace
 }  // namespace mojo