[libwebp] webp_enc_dec: Replace cruncher by lossy alpha encoding (#1838)

* Add new fuzz target for encoding and misc

- Add fuzz_webp_enc_dec and adapt Dockerfile, build.sh
- Lint existing targets
- Add license headers
- Increase fuzz.dict

* webp_enc_dec: Convert input images to inline C arrays

Local files are not available on oss-fuzz servers.

* webp_enc_dec: Fix timeout by skipping crusher

The target fuzz_webp_enc_dec with msan crashes (timeout)
on a 128*128px image encoding with max compression (crusher).
Reduce crusher encoding to 16*16px and below.
Bug report 10423

* webp_enc_dec: Replace cruncher by lossy alpha encoding

The target fuzz_webp_enc_dec with msan crashes (timeout)
during encoding with max compression (cruncher).
Reduce alpha cruncher encoding to 16*16px and below.
Bug report 10634

1 files changed, 4 insertions, 0 deletions

diff --git a/projects/libwebp/fuzz_webp_enc_dec.cc b/projects/libwebp/fuzz_webp_enc_dec.cc
index f50c6c954..993c554f9 100644
--- a/projects/libwebp/fuzz_webp_enc_dec.cc
+++ b/projects/libwebp/fuzz_webp_enc_dec.cc
@@ -186,6 +186,10 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* const data, size_t size) {
       pic.width * pic.height >= 16 * 16) {
     config.lossless = 0;
   }
+  if (config.alpha_quality == 100 && config.method == 6 &&
+      pic.width * pic.height >= 16 * 16) {
+    config.alpha_quality = 99;
+  }
 
   // Encode.
   WebPMemoryWriter memory_writer;