extend gm to test aa[] parameter on xfer4f procs

src/core/SkXfermode4f.cpp

Index: src/core/SkXfermode4f.cpp
diff --git a/src/core/SkXfermode4f.cpp b/src/core/SkXfermode4f.cpp
index 1bf66a2b6998afed75158e842f3ac6b7445783a3..a892ee4c3e25e5e423dc60fffd236e995edbdaef 100644
--- a/src/core/SkXfermode4f.cpp
+++ b/src/core/SkXfermode4f.cpp
@@ -39,10 +39,6 @@ template <DstType D> uint32_t store_dst(const Sk4f& x4) {
     return (D == kSRGB_Dst) ? Sk4f_toS32(x4) : Sk4f_toL32(x4);
 }
 
-static uint32_t linear_unit_to_srgb_32(const Sk4f& l4) {
-    return Sk4f_toL32(l4);
-}
-
 static Sk4f linear_unit_to_srgb_255f(const Sk4f& l4) {
     return linear_to_srgb(l4) * Sk4f(255) + Sk4f(0.5f);
 }
@@ -280,8 +276,8 @@ static void srcover_linear_dst_1(const SkXfermode::PM4fState& state, uint32_t ds
             Sk4f d4 = Sk4f_fromL32(dst[i]);
             Sk4f r4;
             if (a != 0xFF) {
-                s4 = scale_by_coverage(s4, a);
-                r4 = s4 + d4 * Sk4f(1 - get_alpha(s4));
+                Sk4f s4_aa = scale_by_coverage(s4, a);

[mtklein, 2016/02/03 01:32:55]

Ah!  Let's make s4 and dst_scale const?

I guarantee the compiler will allocate registers as well as we can manually if
you just always give each new value a new name.  All the good ones give each new
value a new name internally anyway (this is "SSA" form, single static
assignment).

[reed1, 2016/02/03 03:19:49]

ok

+                r4 = s4_aa + d4 * Sk4f(1 - get_alpha(s4_aa));
             } else {
                 r4 = s4 + d4 * dst_scale;
             }
@@ -323,12 +319,12 @@ static void srcover_srgb_dst_1(const SkXfermode::PM4fState& state, uint32_t dst[
             Sk4f d4 = srgb_4b_to_linear_unit(dst[i]);
             Sk4f r4;
             if (a != 0xFF) {
-                s4 = scale_by_coverage(s4, a);
-                r4 = s4 + d4 * Sk4f(1 - get_alpha(s4));
+                Sk4f s4_aa = scale_by_coverage(s4, a);
+                r4 = s4_aa + d4 * Sk4f(1 - get_alpha(s4_aa));
             } else {
                 r4 = s4 + d4 * dst_scale;
             }
-            dst[i] = linear_unit_to_srgb_32(r4);
+            dst[i] = to_4b(linear_unit_to_srgb_255f(r4));
         }
     } else {
         while (count >= 4) {