libwebp: upstream animation cherry-picks

third_party/libwebp/webp/mux_types.h

Index: third_party/libwebp/webp/mux_types.h
diff --git a/third_party/libwebp/webp/mux_types.h b/third_party/libwebp/webp/mux_types.h
index b8bce363e51533617e65ecfe9f609bec4e8a620d..94d8806e125e2d17d82a36f61dc944d6291bd5f8 100644
--- a/third_party/libwebp/webp/mux_types.h
+++ b/third_party/libwebp/webp/mux_types.h
@@ -26,6 +26,7 @@ extern "C" {
 // the types are left here for reference.
 // typedef enum WebPFeatureFlags WebPFeatureFlags;
 // typedef enum WebPMuxAnimDispose WebPMuxAnimDispose;
+// typedef enum WebPMuxAnimBlend WebPMuxAnimBlend;
 typedef struct WebPData WebPData;
 
 // VP8X Feature Flags.
@@ -45,6 +46,13 @@ typedef enum WebPMuxAnimDispose {
   WEBP_MUX_DISPOSE_BACKGROUND  // Dispose to background color.
 } WebPMuxAnimDispose;
 
+// Blend operation (animation only). Indicates how transparent pixels of the
+// current frame are blended with those of the previous canvas.
+typedef enum WebPMuxAnimBlend {
+  WEBP_MUX_BLEND,              // Blend.
+  WEBP_MUX_NO_BLEND            // Do not blend.
+} WebPMuxAnimBlend;
+
 // Data type used to describe 'raw' data, e.g., chunk data
 // (ICC profile, metadata) and WebP compressed image data.
 struct WebPData {