Handle premultiplication correctly for ColorMatrixColorFilters

bug:17405627

Previously, the input content to the color matrix computation was left
premultiplied. Since the color matrix could reduce the alpha channel,
the alpha was re-multiplied, but this was incomplete, and incorrect.

Instead, apply the color matrix in unpremultiplied space.

Change-Id: I87b8e03d2e228e6ded81f7bbfea952605d7a095c
diff --git a/libs/hwui/Renderer.h b/libs/hwui/Renderer.h
index 6d4bb4a..3681637 100644
--- a/libs/hwui/Renderer.h
+++ b/libs/hwui/Renderer.h
@@ -70,6 +70,7 @@
     // TODO: move to a method on android:Paint
     static inline bool paintWillNotDraw(const SkPaint& paint) {
         return paint.getAlpha() == 0
+                && !paint.getColorFilter()
                 && getXfermode(paint.getXfermode()) != SkXfermode::kClear_Mode;
     }
 
@@ -77,6 +78,7 @@
     static inline bool paintWillNotDrawText(const SkPaint& paint) {
         return paint.getAlpha() == 0
                 && paint.getLooper() == NULL
+                && !paint.getColorFilter()
                 && getXfermode(paint.getXfermode()) == SkXfermode::kSrcOver_Mode;
     }
 // ----------------------------------------------------------------------------