WIP: runtime switch for how to interpret SkColor -vs- srgb

src/core/SkPM4fPriv.h

Index: src/core/SkPM4fPriv.h
diff --git a/src/core/SkPM4fPriv.h b/src/core/SkPM4fPriv.h
index 48fdde7acd0df0ad178f7d5062de751e0452d47f..b75dc71654e9a99023e43f060794186b1b89230a 100644
--- a/src/core/SkPM4fPriv.h
+++ b/src/core/SkPM4fPriv.h
@@ -11,6 +11,8 @@
 #include "SkColorPriv.h"
 #include "SkPM4f.h"
 
+extern bool gTreatSkColorAsSRGB;
+
 static inline float get_alpha(const Sk4f& f4) {
     return f4[SkPM4f::A];
 }
@@ -42,6 +44,14 @@ static inline Sk4f linear_to_srgb(const Sk4f& l4) {
     return set_alpha(l4.sqrt(), get_alpha(l4));
 }
 
+static inline float srgb_to_linear(float x) {
+    return x * x;
+}
+
+static inline float linear_to_srgb(float x) {
+    return sqrtf(x);
+}
+
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 
 static inline Sk4f Sk4f_fromL32(uint32_t src) {