SkImage_Raster's pixels are always immutable.

src/core/SkPixelRef.cpp

Index: src/core/SkPixelRef.cpp
diff --git a/src/core/SkPixelRef.cpp b/src/core/SkPixelRef.cpp
index 6d36915d9afc37e4878ef5bb98dff2f27c03641a..56bcc9a792ff8a6fab70d9f7ff944992b3c1427a 100644
--- a/src/core/SkPixelRef.cpp
+++ b/src/core/SkPixelRef.cpp
@@ -106,7 +106,7 @@ SkPixelRef::SkPixelRef(const SkImageInfo& info)
     fRec.zero();
     fLockCount = 0;
     this->needsNewGenID();
-    fIsImmutable = false;
+    fMutability = kMutable;
     fPreLocked = false;
     fAddedToCache.store(false);
 }
@@ -125,7 +125,7 @@ SkPixelRef::SkPixelRef(const SkImageInfo& info, SkBaseMutex* mutex)
     fRec.zero();
     fLockCount = 0;
     this->needsNewGenID();
-    fIsImmutable = false;
+    fMutability = kMutable;
     fPreLocked = false;
     fAddedToCache.store(false);
 }
@@ -341,7 +341,7 @@ void SkPixelRef::callGenIDChangeListeners() {
 
 void SkPixelRef::notifyPixelsChanged() {
 #ifdef SK_DEBUG
-    if (fIsImmutable) {
+    if (this->isImmutable()) {
         SkDebugf("========== notifyPixelsChanged called on immutable pixelref");
     }
 #endif
@@ -355,7 +355,17 @@ void SkPixelRef::changeAlphaType(SkAlphaType at) {
 }
 
 void SkPixelRef::setImmutable() {
-    fIsImmutable = true;
+    fMutability = kImmutable;
+}
+void SkPixelRef::setTemporarilyImmutable() {
+    SkASSERT(fMutability != kImmutable);
+    fMutability = kTemporarilyImmutable;
+}
+
+void SkPixelRef::restoreMutability() {
+    SkASSERT(fMutability != kImmutable);
+    fMutability = kMutable;

[robertphillips, 2015/07/29 19:26:29]

Hmmm .. can we get rid of the 'notifyPixelsChanged' ?

+    this->notifyPixelsChanged();  // This is just precautionary.
 }
 
 bool SkPixelRef::readPixels(SkBitmap* dst, const SkIRect* subset) {