lottie/parser: updated parser to parse difference mask mode

Change-Id: I607d4f56a849d1cb928926c2d4ecc30cf1313e7e

src/lottie/lottiemodel.h

@@ -587,7 +587,8 @@ public:
       None,
       Add,
       Substarct,
-      Intersect
+      Intersect,
+      Difference
     };
     float opacity(int frameNo) const {return mOpacity.value(frameNo)/100.0;}
     bool isStatic() const {return mIsStatic;}

src/lottie/lottieparser.cpp

@@ -849,6 +849,9 @@ std::shared_ptr<LOTMaskData> LottieParserImpl::parseMaskObject()
             case 'i':
                 obj->mMode = LOTMaskData::Mode::Intersect;
                 break;
+            case 'f':
+                obj->mMode = LOTMaskData::Mode::Difference;
+                break;
             default:
                 obj->mMode = LOTMaskData::Mode::None;
                 break;