SkCodec: add wbmp class

include/codec/SkCodec.h

Index: include/codec/SkCodec.h
diff --git a/include/codec/SkCodec.h b/include/codec/SkCodec.h
index 5a69d1367d69444423c736cbbfbfc0e259c6180f..051564cf734ea0ee0129d5d20e0d73012905ad70 100644
--- a/include/codec/SkCodec.h
+++ b/include/codec/SkCodec.h
@@ -135,20 +135,26 @@ protected:
 
     virtual bool onReallyHasAlpha() const { return false; }
 
+    enum RewindState {
+        kRewound_RewindState,
+        kNoRewindNecessary_RewindState,
+        kCouldNotRewind_RewindState
+    };
     /**
      *  If the stream was previously read, attempt to rewind.
      *  @returns:
-     *      true
-     *       - if the stream needed to be rewound, and the rewind
-     *         succeeded.
-     *       - if the stream did not need to be rewound.
-     *      false
-     *       - if the stream needed to be rewound, and rewind failed.
+     *      kRewound if the stream needed to be rewound, and the
+     *               rewind succeeded.
+     *      kNoRewindNecessary if the stream did not need to be
+     *                         rewound.
+     *      kCouldNotRewind if the stream needed to be rewound, and
+     *                      rewind failed.
+     *
      *  Subclasses MUST call this function before reading the stream (e.g. in
      *  onGetPixels). If it returns false, onGetPixels should return

[scroggo, 2015/03/26 20:29:44]

false -> kCouldNotRewind.

If it returns kRewound, the stream is back at the beginning, and needs to be
advanced to the point where we are ready to call getPixels (e.g. the header
needs to be read/skipped).

Maybe the names should not reflect rewinding, but where the exact location of
the stream is. Maybe something like:

kBeginning
kEndofHeader (although an SkCodec may read more than the header, this
              seems fairly descriptive)
kUndetermined - or something else? This means we don't know how to
                proceed, so we have to return kCouldNotRewind.

[hal.canary, 2015/03/26 21:46:09]

Let's leave it as is.  You can change it in the future if you like.

      *  kCouldNotRewind.
      */
-    bool SK_WARN_UNUSED_RESULT rewindIfNeeded();
+    RewindState SK_WARN_UNUSED_RESULT rewindIfNeeded();
 
     /*
      *