Disable net_url_request_fuzzer on builds for ClusterFuzz

The fuzzer's corpus grows too large (10 GB). Disable it on ClusterFuzz
until it can be figured out why.

Bug: 820089
Change-Id: Ic9ef393dae9e27e13398817e2dfb9d6df3a40067
Reviewed-on: https://chromium-review.googlesource.com/956102
Commit-Queue: Jonathan Metzman <metzman@chromium.org>
Reviewed-by: Jonathan Metzman <metzman@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542000}

net/BUILD.gn

@@ -6227,6 +6227,10 @@ fuzzer_test("net_url_request_fuzzer") {
     "//net",
   ]
   dict = "data/fuzzer_dictionaries/net_url_request_fuzzer.dict"
+
+  # TODO(crbug.com/820089): Figure out why this fuzzer's corpus explodes to
+  # 10 GB. For now, disable it on ClusterFuzz.
+  additional_configs = [ "//testing/libfuzzer:no_clusterfuzz" ]
 }
 
 fuzzer_test("net_auth_challenge_tokenizer_fuzzer") {