Fill incomplete images in SkCodec parent class

src/codec/SkWebpCodec.cpp

Index: src/codec/SkWebpCodec.cpp
diff --git a/src/codec/SkWebpCodec.cpp b/src/codec/SkWebpCodec.cpp
index ccf49649edb30e669c1b497f94b0e3cb69eeec0d..d53828dca45335e1fcac1e8ac2dd31bdc4ad74be 100644
--- a/src/codec/SkWebpCodec.cpp
+++ b/src/codec/SkWebpCodec.cpp
@@ -151,7 +151,8 @@ bool SkWebpCodec::onGetValidSubset(SkIRect* desiredSubset) const {
 }
 
 SkCodec::Result SkWebpCodec::onGetPixels(const SkImageInfo& dstInfo, void* dst, size_t rowBytes,
-                                         const Options& options, SkPMColor*, int*) {
+                                         const Options& options, SkPMColor*, int*,
+                                         int* incompleteScanlines) {
     if (!this->rewindIfNeeded()) {
         return kCouldNotRewind;
     }
@@ -231,10 +232,10 @@ SkCodec::Result SkWebpCodec::onGetPixels(const SkImageInfo& dstInfo, void* dst,
     while (true) {
         const size_t bytesRead = stream()->read(buffer, BUFFER_SIZE);
         if (0 == bytesRead) {
-            // FIXME: Maybe this is an incomplete image? How to decide? Based
-            // on the number of rows decoded? We can know the number of rows
-            // decoded using WebPIDecGetRGB.
-            return kInvalidInput;
+            int rowsDecoded;
+            WebPIDecGetRGB(idec, &rowsDecoded, NULL, NULL, NULL);
+            *incompleteScanlines = dstDimensions.height() - rowsDecoded;
+            return kIncompleteInput;
         }
 
         switch (WebPIAppend(idec, buffer, bytesRead)) {