Convert SkPMFloat to [0,1] range and prune its API.

src/core/SkPMFloat.h

Index: src/core/SkPMFloat.h
diff --git a/src/core/SkPMFloat.h b/src/core/SkPMFloat.h
index ce7b75e705f002c91c224e53f077e72e16d0b7c3..f1d302458d0fe121e0950b8b08628c60283bb893 100644
--- a/src/core/SkPMFloat.h
+++ b/src/core/SkPMFloat.h
@@ -21,15 +21,12 @@
 namespace {
 
 // A pre-multiplied color storing each component in the same order as SkPMColor,
-// but as a float in the range [0, 255].
+// but as a float in the range [0, 1].
 class SkPMFloat : public Sk4f {
 public:
     static SkPMFloat FromPMColor(SkPMColor c) { return SkPMFloat(c); }
     static SkPMFloat FromARGB(float a, float r, float g, float b) { return SkPMFloat(a,r,g,b); }
 
-    // May be more efficient than one at a time.  No special alignment assumed for SkPMColors.
-    static void From4PMColors(const SkPMColor[4], SkPMFloat*, SkPMFloat*, SkPMFloat*, SkPMFloat*);
-
     // Uninitialized.
     SkPMFloat() {}
     explicit SkPMFloat(SkPMColor);
@@ -47,24 +44,10 @@ public:
     float g() const { return this->kth<SK_G32_SHIFT / 8>(); }
     float b() const { return this->kth<SK_B32_SHIFT / 8>(); }
 
-    // N.B. All methods returning an SkPMColor call SkPMColorAssert on that result before returning.
-
-    // round() and roundClamp() round component values to the nearest integer.
-    SkPMColor round() const;  // Assumes all values in [0, 255].  Some implementations may clamp.
-    SkPMColor roundClamp() const;  // Will clamp all values to [0, 255].
-
-    // Like round(), but truncates instead of rounding.
-    // The domain of this function is (-1.0f, 256.0f).  Values in (-1.0f, 0.0f] trunc to a zero.
-    SkPMColor trunc() const;
-
-    // 4-at-a-time versions of round() and roundClamp(). Like From4PMColors(), no alignment assumed.
-    static void RoundTo4PMColors(
-            const SkPMFloat&, const SkPMFloat&, const SkPMFloat&, const SkPMFloat&, SkPMColor[4]);
-    static void RoundClampTo4PMColors(
-            const SkPMFloat&, const SkPMFloat&, const SkPMFloat&, const SkPMFloat&, SkPMColor[4]);
+    SkPMColor round() const;  // Rounds from [0.0f, 1.0f] to [0, 255], clamping if out of range.
 
     bool isValid() const {
-        return this->a() >= 0 && this->a() <= 255
+        return this->a() >= 0 && this->a() <= 1
             && this->r() >= 0 && this->r() <= this->a()
             && this->g() >= 0 && this->g() <= this->a()
             && this->b() >= 0 && this->b() <= this->a();
@@ -80,10 +63,8 @@ private:
     // Platform implementations of SkPMFloat assume Sk4f uses SSE or NEON.  _none is generic.
     #include "../opts/SkPMFloat_none.h"
 #else
-    #if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSSE3
-        #include "../opts/SkPMFloat_SSSE3.h"
-    #elif SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2
-        #include "../opts/SkPMFloat_SSE2.h"
+    #if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2
+        #include "../opts/SkPMFloat_sse.h"
     #elif defined(SK_ARM_HAS_NEON)
         #include "../opts/SkPMFloat_neon.h"
     #else