libwebp: update to 0.5.0

third_party/libwebp/dec/webpi.h

Index: third_party/libwebp/dec/webpi.h
diff --git a/third_party/libwebp/dec/webpi.h b/third_party/libwebp/dec/webpi.h
index 457c72eda4851aa66cac290391263e81c1a3b2dc..c75a2e4a5bfdda942143bc56f5a5ebf1a6b67db1 100644
--- a/third_party/libwebp/dec/webpi.h
+++ b/third_party/libwebp/dec/webpi.h
@@ -26,7 +26,10 @@ extern "C" {
 
 typedef struct WebPDecParams WebPDecParams;
 typedef int (*OutputFunc)(const VP8Io* const io, WebPDecParams* const p);
-typedef int (*OutputRowFunc)(WebPDecParams* const p, int y_pos);
+typedef int (*OutputAlphaFunc)(const VP8Io* const io, WebPDecParams* const p,
+                               int expected_num_out_lines);
+typedef int (*OutputRowFunc)(WebPDecParams* const p, int y_pos,
+                             int max_out_lines);
 
 struct WebPDecParams {
   WebPDecBuffer* output;             // output buffer.
@@ -40,7 +43,7 @@ struct WebPDecParams {
   void* memory;                  // overall scratch memory for the output work.
 
   OutputFunc emit;               // output RGB or YUV samples
-  OutputFunc emit_alpha;         // output alpha channel
+  OutputAlphaFunc emit_alpha;    // output alpha channel
   OutputRowFunc emit_alpha_row;  // output one line of rescaled alpha values
 };