Add snappy compress fuzzer.

Also, rename snappy_fuzzer to snappy_uncompress_fuzzer.

R=mmoroz@chromium.org,pwnall@chromium.org

Bug: 900481
Change-Id: I83fa8be129f34dc2cbed4a21492139cea32c2044
Reviewed-on: https://chromium-review.googlesource.com/c/1337811
Commit-Queue: Abhishek Arya <inferno@chromium.org>
Reviewed-by: Max Moroz <mmoroz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608584}

testing/libfuzzer/fuzzers/BUILD.gn

@@ -40,13 +40,25 @@ fuzzer_test("language_detection_fuzzer") {
   ]
 }
 
-fuzzer_test("snappy_fuzzer") {
+fuzzer_test("snappy_compress_fuzzer") {
   sources = [
-    "snappy_fuzzer.cc",
+    "snappy_compress_fuzzer.cc",
+  ]
+  deps = [
+    "//base",
+    "//third_party/snappy:snappy",
+  ]
+  seed_corpus = "//third_party/snappy/src/testdata"
+}
+
+fuzzer_test("snappy_uncompress_fuzzer") {
+  sources = [
+    "snappy_uncompress_fuzzer.cc",
   ]
   deps = [
     "//third_party/snappy:snappy",
   ]
+  seed_corpus = "//third_party/snappy/src/testdata"
 }
 
 fuzzer_test("template_url_parser_fuzzer") {

testing/libfuzzer/fuzzers/snappy_compress_fuzzer.cc

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/logging.h"
+#include "third_party/snappy/src/snappy.h"
+
+// Entry point for LibFuzzer.
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  const char* uncompressed = reinterpret_cast<const char*>(data);
+  std::string compressed;
+  snappy::Compress(uncompressed, size, &compressed);
+  CHECK(snappy::IsValidCompressedBuffer(compressed.data(), compressed.size()));
+
+  std::string uncompressed_after_compress;
+  CHECK(snappy::Uncompress(compressed.data(), compressed.size(),
+                           &uncompressed_after_compress));
+  CHECK_EQ(uncompressed_after_compress, std::string(uncompressed, size));
+
+  return 0;
+}