Added ASSERT_SIZE macro for checking size of size-sensitive classes

third_party/WebKit/Source/wtf/SizeAssertions.h

Index: third_party/WebKit/Source/wtf/SizeAssertions.h
diff --git a/third_party/WebKit/Source/wtf/SizeAssertions.h b/third_party/WebKit/Source/wtf/SizeAssertions.h
new file mode 100644
index 0000000000000000000000000000000000000000..d321392ba1bdfd09b217ce66018c9af51bd40c49
--- /dev/null
+++ b/third_party/WebKit/Source/wtf/SizeAssertions.h
@@ -0,0 +1,25 @@
+#ifndef WTF_SizeAssertions_h

[esprehn, 2016/09/08 22:25:28]

missing the short copyright header

[sashab, 2016/09/09 01:23:47]

Thanks! Also removed unused #include below.

Still bummed we can't have compile error messages like
"CSSValue is %d bytes, expected it to be %d bytes"
It's too bad static_assert doesn't allow parametrized strings :'(

+#define WTF_SizeAssertions_h
+
+#include "wtf/CPU.h"
+
+namespace WTF {
+
+// The ASSERT_SIZE macro can be used to check that a given struct is the same
+// size as a class. This is useful to visualize where the space is being used in
+// a class, as well as give a useful compile error message when the size doesn't
+// match the expected value.
+template<class T, class U> struct assert_size {
+    template<int ActualSize, int ExpectedSize> struct assertSizeEqual {
+        static_assert(ActualSize == ExpectedSize, "Class should stay small");
+        static const bool innerValue = true;
+    };
+    static const bool value = assertSizeEqual<sizeof(T), sizeof(U)>::innerValue;
+};
+
+} // namespace WTF
+
+#define ASSERT_SIZE(className, sameSizeAsClassName) \
+    static_assert(WTF::assert_size<className, sameSizeAsClassName>::value, "");
+
+#endif // WTF_SizeAssertions_h