Make a workaround for VS2012 update 3 optimizer bug.

VS2012 has a optimizer bug that wrongly optimize "toASCIILower" in wtf/ASCIICType.h, we use "+ 0x20" instead of " << 5".

BUG=268215

Review URL: https://chromiumcodereview.appspot.com/21934003

git-svn-id: svn://svn.chromium.org/blink/trunk@155570 bbb929c8-8fbe-4397-9dbb-9b2b20218538