Added ASSERT_SIZE macro for checking size of size-sensitive classes

third_party/WebKit/Source/wtf/SizeAssertions.h

+#ifndef WTF_SizeAssertions_h
+#define WTF_SizeAssertions_h
+
+#include "wtf/CPU.h"
+
+namespace WTF {
+
+// Expected32BitSize and Expected64BitSize are in bytes. Use a template instead
+// of a plain static assert so that failure messages give the expected number.
+template<class T, int Expected32BitSize, int Expected64BitSize> struct assert_size {
+    template<int ActualSize, int ExpectedSize> class assertSizeEqual {
+        static_assert(ActualSize == ExpectedSize,
+            "Object size doesn't match expected value, think before making it bigger :-)");
+    };
+#if CPU(32BIT)
+    assertSizeEqual<sizeof(T), Expected32BitSize> tmp;
+#else
+    assertSizeEqual<sizeof(T), Expected64BitSize> tmp;
+#endif
+    enum { Dummy = 1 };
+};
+
+} // namespace WTF
+
+// Some objects have additional members when asserts are enabled, so only check
+// sizes when they are disabled.
+#if ENABLE(ASSERT)

[esprehn, 2016/08/11 09:47:40]

The bots and CQ always enable asserts, so this means you're never checking sizes
in the CQ. I don't think we want that.

+#define ASSERT_SIZE(className, expected32BitSize, expected64BitSize)
+#else
+#define ASSERT_SIZE(className, expected32BitSize, expected64BitSize) \
+    static_assert(WTF::assert_size<className, expected32BitSize, expected64BitSize>::Dummy, "");
+#endif
+
+#endif // WTF_SizeAssertions_h