Templatize SkPMFloat to support both 1 and 255 biases.

src/opts/SkPMFloat_neon.h

Index: src/opts/SkPMFloat_neon.h
diff --git a/src/opts/SkPMFloat_neon.h b/src/opts/SkPMFloat_neon.h
index 4e099f91ecce2593719c211a32bf408bcac2bf1b..aeb1a70a5b86bb9376db37e3f9e8d6799dcfc5ea 100644
--- a/src/opts/SkPMFloat_neon.h
+++ b/src/opts/SkPMFloat_neon.h
@@ -9,18 +9,28 @@ namespace { // See SkPMFloat.h
 
 static_assert(SK_A32_SHIFT == 24, "This file assumes little-endian.");
 
-inline SkPMFloat::SkPMFloat(SkPMColor c) {
+template <int kBias>
+inline SkPMFloat<kBias>::SkPMFloat(SkPMColor c) {
     SkPMColorAssert(c);
     uint8x8_t   fix8    = (uint8x8_t)vdup_n_u32(c);
     uint16x8_t  fix8_16 = vmovl_u8(fix8);
     uint32x4_t  fix8_32 = vmovl_u16(vget_low_u16(fix8_16));
-    fVec = vmulq_f32(vcvtq_f32_u32(fix8_32), vdupq_n_f32(1.0f/255));
+    fVec = vcvtq_f32_u32(fix8_32);
+    if (kBias == 1) {
+        fVec = vmulq_f32(fVec, vdupq_n_f32(1.0f/255));
+    }
     SkASSERT(this->isValid());
 }
 
-inline SkPMColor SkPMFloat::round() const {
+template <int kBias>
+inline SkPMColor SkPMFloat<kBias>::round() const {
     // vcvt_u32_f32 truncates, so we round manually by adding a half before converting.
-    float32x4_t rounded = vmlaq_f32(vdupq_n_f32(0.5f), fVec, vdupq_n_f32(255));
+    float32x4_t rounded;
+    if (kBias == 1) {
+        rounded = vmlaq_f32(vdupq_n_f32(0.5f), fVec, vdupq_n_f32(255));
+    } else {
+        rounded = vaddq_f32(vdupq_n_f32(0.5f), fVec);
+    }
     uint32x4_t  fix8_32 = vcvtq_u32_f32(rounded);
     uint16x4_t  fix8_16 = vqmovn_u32(fix8_32);
     uint8x8_t   fix8    = vqmovn_u16(vcombine_u16(fix8_16, vdup_n_u16(0)));
@@ -29,11 +39,13 @@ inline SkPMColor SkPMFloat::round() const {
     return c;
 }
 
-inline Sk4f SkPMFloat::alphas() const {
+template <int kBias>
+inline Sk4f SkPMFloat<kBias>::alphas() const {
     return vdupq_lane_f32(vget_high_f32(fVec), 1);  // Duplicate high lane of high half i.e. lane 3.
 }
 
-inline SkPMFloat SkPMFloat::FromOpaqueColor(SkColor c) {
+template <int kBias>
+inline SkPMFloat<kBias> SkPMFloat<kBias>::FromOpaqueColor(SkColor c) {
     SkASSERT(SkColorGetA(c) == 0xFF);
     uint8x8_t fix8 = (uint8x8_t)vdup_n_u32(c);
 #if defined(SK_PMCOLOR_IS_RGBA)
@@ -42,7 +54,11 @@ inline SkPMFloat SkPMFloat::FromOpaqueColor(SkColor c) {
     uint16x8_t fix8_16 = vmovl_u8(fix8);
     uint32x4_t fix8_32 = vmovl_u16(vget_low_u16(fix8_16));
 
-    SkPMFloat pmf = Sk4f(vmulq_f32(vcvtq_f32_u32(fix8_32), vdupq_n_f32(1.0f/255)));
+    float32x4_t floats = vcvtq_f32_u32(fix8_32);
+    if (kBias == 1) {
+        floats = vmulq_f32(floats, vdupq_n_f32(1.0f/255));
+    }
+    SkPMFloat pmf = Sk4f(floats);
     SkASSERT(pmf.isValid());
     return pmf;
 }