move erase into SkPixmap

include/core/SkPixmap.h

Index: include/core/SkPixmap.h
diff --git a/include/core/SkPixmap.h b/include/core/SkPixmap.h
index 913d007c4dc98d82a4d5c51db4a65e62de684db9..a32b40c58d434cd6e007e81e3698f3da22500339 100644
--- a/include/core/SkPixmap.h
+++ b/include/core/SkPixmap.h
@@ -133,6 +133,14 @@ public:
         return this->readPixels(dst.info(), dst.writable_addr(), dst.rowBytes(), 0, 0);
     }
 
+    /**
+     *  Returns true if pixels were written to (e.g. if colorType is kUnknown_SkColorType, this
+     *  will return false). If subset does not intersect the bounds of this pixmap, returns false.
+     */
+    bool erase(SkColor, const SkIRect& subset) const;
+
+    bool erase(SkColor color) const { return this->erase(color, this->bounds()); }
+
 private:
     const void*     fPixels;
     SkColorTable*   fCTable;
@@ -165,8 +173,34 @@ public:
      */
     void alloc(const SkImageInfo&);
 
+    // We wrap these so we can clear our internal storage
+
+    void reset() {
+        this->freeStorage();
+        this->INHERITED::reset();
+    }
+    void reset(const SkImageInfo& info, const void* addr, size_t rb, SkColorTable* ctable = NULL) {
+        this->freeStorage();
+        this->INHERITED::reset(info, addr, rb, ctable);
+    }
+    void reset(const SkImageInfo& info) {
+        this->freeStorage();
+        this->INHERITED::reset(info);
+    }
+    bool SK_WARN_UNUSED_RESULT reset(const SkMask& mask) {
+        this->freeStorage();
+        return this->INHERITED::reset(mask);
+    }
+
 private:
     void*   fStorage;
+
+    void freeStorage() {
+        sk_free(fStorage);
+        fStorage = NULL;
+    }
+
+    typedef SkPixmap INHERITED;
 };
 
 /////////////////////////////////////////////////////////////////////////////////////////////