Add SK_BEGIN_REQUIRE_DENSE / SK_END_REQUIRE_DENSE.

include/core/SkTypes.h

Index: include/core/SkTypes.h
diff --git a/include/core/SkTypes.h b/include/core/SkTypes.h
index d9254acf5f776d8abda7b8d3486d834fcaa6e200..5720c30970e5d2ce1ad9f69922caa6a32eeb1163 100644
--- a/include/core/SkTypes.h
+++ b/include/core/SkTypes.h
@@ -287,6 +287,16 @@ static inline bool SkIsU16(long x) {
 template <typename T, size_t N> char (&SkArrayCountHelper(T (&array)[N]))[N];
 #define SK_ARRAY_COUNT(array) (sizeof(SkArrayCountHelper(array)))
 
+// Can be used to bracket data types that must be dense, e.g. hash keys.
+#if defined(__clang__)  // This should work on GCC too, but GCC diagnostic pop didn't seem to work!
+    #define SK_BEGIN_REQUIRE_DENSE _Pragma("GCC diagnostic push") \
+                                   _Pragma("GCC diagnostic error \"-Wpadded\"")
+    #define SK_END_REQUIRE_DENSE   _Pragma("GCC diagnostic pop")
+#else
+    #define SK_BEGIN_REQUIRE_DENSE
+    #define SK_END_REQUIRE_DENSE
+#endif
+
 #define SkAlign2(x)     (((x) + 1) >> 1 << 1)
 #define SkIsAlign2(x)   (0 == ((x) & 1))