Update libwebp and resume testing scaled webp

dm/DM.cpp

Index: dm/DM.cpp
diff --git a/dm/DM.cpp b/dm/DM.cpp
index 9dcdff1a0fce6f98f10228d33595e618a31f4c2e..0faa3e4a50f73d0a507f10acddb1113b8206063e 100644
--- a/dm/DM.cpp
+++ b/dm/DM.cpp
@@ -215,11 +215,6 @@ static void push_codec_srcs(Path path) {
     const float scales[] = { 0.125f, 0.25f, 0.375f, 0.5f, 0.625f, 0.750f, 0.875f, 1.0f };
 
     for (float scale : scales) {
-        if (scale != 1.0f && (path.endsWith(".webp") || path.endsWith(".WEBP"))) {
-            // FIXME: skbug.com/4038 Scaling webp seems to leave some pixels uninitialized/
-            // compute their colors based on uninitialized values.
-            continue;
-        }
         // Build additional test cases for images that decode natively to non-canvas types
         switch(codec->getInfo().colorType()) {
             case kGray_8_SkColorType: