Exposing the isImmutable/setImmutable API of SkPixelRef in SkBitmap

REVIEW=http://codereview.appspot.com/5491055/



git-svn-id: http://skia.googlecode.com/svn/trunk@2883 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/core/SkBitmap.cpp b/src/core/SkBitmap.cpp
index 24a1839..2376dd3 100644
--- a/src/core/SkBitmap.cpp
+++ b/src/core/SkBitmap.cpp
@@ -409,6 +409,7 @@
 }
 
 void SkBitmap::notifyPixelsChanged() const {
+    SkASSERT(!this->isImmutable());
     if (fPixelRef) {
         fPixelRef->notifyPixelsChanged();
     } else {
@@ -504,6 +505,19 @@
 
 ///////////////////////////////////////////////////////////////////////////////
 
+bool SkBitmap::isImmutable() const { 
+    return fPixelRef ? fPixelRef->isImmutable() :
+        fFlags & kImageIsImmutable_Flag; 
+}
+
+void SkBitmap::setImmutable() {
+    if (fPixelRef) {
+        fPixelRef->setImmutable();
+    } else {
+        fFlags |= kImageIsImmutable_Flag;
+    }
+}
+
 bool SkBitmap::isOpaque() const {
     switch (fConfig) {
         case kNo_Config: