SkPMFloat: avoid loads and stores where possible.

src/opts/SkPMFloat_none.h

-#include "SkColorPriv.h"
+inline SkPMFloat& SkPMFloat::operator=(const SkPMFloat& that) {
+    for (int i = 0; i < 4; i++) { fColor[i] = that.fColor[i]; }
+    return *this;
+}
 
 inline SkPMFloat::SkPMFloat(SkPMColor c) {
     *this = SkPMFloat::FromARGB(SkGetPackedA32(c),
                                 SkGetPackedR32(c),
                                 SkGetPackedG32(c),
                                 SkGetPackedB32(c));
     SkASSERT(this->isValid());
 }
 
 inline SkPMColor SkPMFloat::get() const {
@@ skipping 17 matching lines @@
     for (int i = 0; i < 4; i++) { floats[i] = FromPMColor(colors[i]); }
 }
 
 inline void SkPMFloat::To4PMColors(SkPMColor colors[4], const SkPMFloat floats[4]) {
     for (int i = 0; i < 4; i++) { colors[i] = floats[i].get(); }
 }
 
 inline void SkPMFloat::ClampTo4PMColors(SkPMColor colors[4], const SkPMFloat floats[4]) {
     for (int i = 0; i < 4; i++) { colors[i] = floats[i].clamped(); }
 }