add optional SkAlphaType parameter to notifyPixelsChanged

src/core/SkPixelRef.cpp

Index: src/core/SkPixelRef.cpp
diff --git a/src/core/SkPixelRef.cpp b/src/core/SkPixelRef.cpp
index 10e1309c0b1af377268a0bdb30f4de2f9b61dee3..5fcfabc3aca12879963e6811e8d6b3c3a9dadeb9 100644
--- a/src/core/SkPixelRef.cpp
+++ b/src/core/SkPixelRef.cpp
@@ -264,6 +264,14 @@ void SkPixelRef::notifyPixelsChanged() {
     this->needsNewGenID();
 }
 
+void SkPixelRef::notifyAlphaTypeChanged(SkAlphaType at) {
+    if (fInfo.fAlphaType != at) {
+        *const_cast<SkAlphaType*>(&fInfo.fAlphaType) = at;
+        this->callGenIDChangeListeners();

[scroggo, 2014/01/24 20:50:52]

I kind of think these two functions should be the same (or perhaps one should
call the other). The only time we call one but not the other is in the
destructor, when we don't need to call needsNewGenID, but setting two fields
needlessly might be a low price to pay to ensure we never accidentally call one
without the other.

[reed1, 2014/01/27 13:46:14]

I'll sync with the GPU guys, who invented this pattern I think.

+        this->needsNewGenID();
+    }
+}
+
 void SkPixelRef::setImmutable() {
     fIsImmutable = true;
 }