Factor out UnPreMultiplyPreservingByteOrder

src/core/SkUnPreMultiply.cpp

Index: src/core/SkUnPreMultiply.cpp
diff --git a/src/core/SkUnPreMultiply.cpp b/src/core/SkUnPreMultiply.cpp
index ad87f8af1442060e6a42d9cadc357a2e0d3c9b76..6245e96429cd3e00751855d60a21a16f33a55a70 100644
--- a/src/core/SkUnPreMultiply.cpp
+++ b/src/core/SkUnPreMultiply.cpp
@@ -17,6 +17,15 @@ SkColor SkUnPreMultiply::PMColorToColor(SkPMColor c) {
                           ApplyScale(scale, SkGetPackedB32(c)));
 }
 
+uint32_t SkUnPreMultiply::UnPreMultiplyPreservingByteOrder(SkPMColor c) {
+    const U8CPU a = SkGetPackedA32(c);
+    const Scale scale = GetScale(a);
+    return SkPackARGB32NoCheck(a,
+                               ApplyScale(scale, SkGetPackedR32(c)),
+                               ApplyScale(scale, SkGetPackedG32(c)),
+                               ApplyScale(scale, SkGetPackedB32(c)));
+}
+
 const uint32_t SkUnPreMultiply::gTable[] = {
     0x00000000, 0xFF000000, 0x7F800000, 0x55000000, 0x3FC00000, 0x33000000, 0x2A800000, 0x246DB6DB,
     0x1FE00000, 0x1C555555, 0x19800000, 0x172E8BA3, 0x15400000, 0x139D89D9, 0x1236DB6E, 0x11000000,