Merge commit '67653bbe50841153bfeaebcc5792bd8464da9880' as 'external/libwebp/libwebp'

external/libwebp/libwebp/tests/README.md

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+# Tests
+
+This is a collection of tests for the libwebp libraries, currently covering
+fuzzing through the APIs. Additional test vector coverage can be found at:
+https://chromium.googlesource.com/webm/libwebp-test-data
+
+## Building
+
+### Fuzzers
+
+Follow the [build instructions](../doc/building.md) for libwebp, optionally
+adding build flags for various sanitizers (e.g., -fsanitize=address).
+
+`fuzzer/makefile.unix` can then be used to compile the fuzzer targets:
+
+```shell
+$ make -C fuzzer -f makefile.unix
+```