SkBitmap::scrollRect changes pixels, but only if not immutable.

scrollRect will now return false if the bitmap is immutable, and
call notifyPixelsChanged when changing the pixels. This will give
the bitmap a new generation ID.

Review URL: https://codereview.appspot.com/6480046

git-svn-id: http://skia.googlecode.com/svn/trunk@5230 2bbb7eff-a529-9590-31e7-b0007b416f81

include/core/SkBitmap.h

@@ -395,7 +395,8 @@ public:
 
     /** Scroll (a subset of) the contents of this bitmap by dx/dy. If there are
         no pixels allocated (i.e. getPixels() returns null) the method will
-        still update the inval region (if present).
+        still update the inval region (if present). If the bitmap is immutable,
+        do nothing and return false.
 
         @param subset The subset of the bitmap to scroll/move. To scroll the
                       entire contents, specify [0, 0, width, height] or just

src/core/SkBitmap_scroll.cpp

@@ -11,6 +11,10 @@
 bool SkBitmap::scrollRect(const SkIRect* subset, int dx, int dy,
                           SkRegion* inval) const
 {
+    if (this->isImmutable()) {
+        return false;
+    }
+
     if (NULL != subset) {
         SkBitmap tmp;
 
@@ -113,5 +117,7 @@ bool SkBitmap::scrollRect(const SkIRect* subset, int dx, int dy,
         dst += rowBytes;
         src += rowBytes;
     }
+
+    this->notifyPixelsChanged();
     return true;
 }