Add an option to create unpremultiplied bitmaps.

src/core/SkColor.cpp

Index: src/core/SkColor.cpp
diff --git a/src/core/SkColor.cpp b/src/core/SkColor.cpp
index 6fa239ff539399eb0b061348ee0f0170f014cd97..3f503dd977ec7a5cd855b4fbba229003e769780f 100644
--- a/src/core/SkColor.cpp
+++ b/src/core/SkColor.cpp
@@ -19,6 +19,14 @@ SkPMColor SkPreMultiplyColor(SkColor c) {
                                    SkColorGetG(c), SkColorGetB(c));
 }
 
+SkPMColor SkPreMultiplyUnPMColor(SkUnPMColor c) {
+    U8CPU a = SkGetPackedA32(c);
+    U8CPU r = SkGetPackedR32(c);
+    U8CPU g = SkGetPackedG32(c);
+    U8CPU b = SkGetPackedB32(c);
+    return SkPreMultiplyARGB(a, r, g, b);
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 static inline SkScalar ByteToScalar(U8CPU x) {