IWYU: Include all headers for symbols used in files.

Semi-automatically taking the the misc-include-cleaner warnings
by clang-tidy and fixing files to be self-contained.

Change-Id: Iaaa2b2ec9d6dcce547fa5cb6b4f056dfc8c781ff

examples/dwebp.c

@@ -25,6 +25,8 @@
 #include "../imageio/webpdec.h"
 #include "./stopwatch.h"
 #include "./unicode.h"
+#include "webp/decode.h"
+#include "webp/types.h"
 
 static int verbose = 0;
 static int quiet = 0;