rebaseline_server: use just skpdiff, not Python Image Library

tools/skpdiff/SkImageDiffer.h

Index: tools/skpdiff/SkImageDiffer.h
diff --git a/tools/skpdiff/SkImageDiffer.h b/tools/skpdiff/SkImageDiffer.h
index 641bbe8f8f863b4610348b5b41573564e21fc88b..1f9ffd1886b52e5eb2feba7f1b0c5ab32c8adfd1 100644
--- a/tools/skpdiff/SkImageDiffer.h
+++ b/tools/skpdiff/SkImageDiffer.h
@@ -24,10 +24,30 @@ public:
     struct Result {
         double result;
         int poiCount;
+        // TODO(djsollen): Figure out a way that the differ can report which of the
+        // optional fields it has filled in.  See http://skbug.com/2712 ('allow
+        // skpdiff to report different sets of result fields for different comparison algorithms')
         SkBitmap poiAlphaMask; // optional
+        SkBitmap rgbDiffBitmap; // optional
+        SkBitmap whiteDiffBitmap; // optional
+        int maxRedDiff; // optional
+        int maxGreenDiff; // optional
+        int maxBlueDiff; // optional
         double timeElapsed; // optional
     };
 
+    // A bitfield indicating which bitmap types we want a differ to create.
+    //
+    // TODO(epoger): Remove whiteDiffBitmap, because alphaMask can provide
+    // the same functionality and more.
+    // It will be a little bit tricky, because the rebaseline_server client
+    // and server side code will both need to change to use the alphaMask.
+    struct BitmapsToCreate {
+        bool alphaMask;
+        bool rgbDiff;
+        bool whiteDiff;
+    };
+
     /**
      * Gets a unique and descriptive name of this differ
      * @return A statically allocated null terminated string that is the name of this differ
@@ -43,10 +63,10 @@ public:
      * diff on a pair of bitmaps.
      * @param  baseline    The correct bitmap
      * @param  test        The bitmap whose difference is being tested
-     * @param  computeMask true if the differ is to attempt to create poiAlphaMask
+     * @param  bitmapsToCreate  Which bitmaps the differ should attempt to create
      * @return             true on success, and false in the case of failure
      */
-    virtual bool diff(SkBitmap* baseline, SkBitmap* test, bool computeMask,
+    virtual bool diff(SkBitmap* baseline, SkBitmap* test, const BitmapsToCreate& bitmapsToCreate,
                       Result* result) const = 0;
 };