Upgrade AlignedMemory to support dynamic allocations.

base/compiler_specific.h

Index: base/compiler_specific.h
diff --git a/base/compiler_specific.h b/base/compiler_specific.h
index 64273a98db93c4fc0158690958bc7cd4de225d32..1704c4cc156744d2c9bd6db5291830ceec8a08dc 100644
--- a/base/compiler_specific.h
+++ b/base/compiler_specific.h
@@ -114,11 +114,13 @@
 #define ALIGNAS(byte_alignment) __attribute__((aligned(byte_alignment)))
 #endif
 
-// Return the byte alignment of the given type (available at compile time).
+// Return the byte alignment of the given type (available at compile time).  Use
+// sizeof(type) prior to checking __alignof to workaround Visual C++ bug:
+// http://connect.microsoft.com/VisualStudio/feedback/details/682695/c-alignof-fails-to-properly-evalute-alignment-of-dependent-types
 // Use like:
 //   ALIGNOF(int32)  // this would be 4
 #if defined(COMPILER_MSVC)
-#define ALIGNOF(type) __alignof(type)
+#define ALIGNOF(type) (sizeof(type) - sizeof(type) + __alignof(type))
 #elif defined(COMPILER_GCC)
 #define ALIGNOF(type) __alignof__(type)
 #endif