MSE: Remove close_fd_mask suppression for MSE fuzzers

With https://chromium-review.googlesource.com/c/chromium/src/+/1371020
landed, MSE pipeline_integration_fuzzers no longer appear to emit
spurious gtest failure messages.

However, the non-MSE (SRC=) media_pipeline_integration_fuzzer still
emits such messages.

This change narrows the close_fd_mask=1 libfuzzer option to no longer be
used for the MSE fuzzers. It remains for the SRC
pipeline_integration_fuzzer until the underlying spurious gtest messages
are fixed.

BUG=894460
TEST=Local build of MSE pipeline integration fuzzers does not produce
options files, but SRC fuzzer still does.

Change-Id: I1bcd642892fd909dbd1f9c639ae9a58cac4cad0f
Reviewed-on: https://chromium-review.googlesource.com/c/1373034Reviewed-by: Jonathan Metzman <metzman@chromium.org>
Commit-Queue: Matthew Wolenetz <wolenetz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615962}

media/test/BUILD.gn

@@ -220,10 +220,12 @@ foreach(variant, pipeline_integration_fuzzer_variants) {
       "//ui/gfx:test_support",
     ]
 
-    libfuzzer_options = [
-      # This is done to suppress tons of log messages generated by gmock asserts.
-      "close_fd_mask=1",
-    ]
+    # This is done to suppress tons of log messages generated by gmock asserts.
+    # TODO(wolenetz): Modify media_pipeline_integration_fuzzer to not fail
+    # spurious gtest asserts. See https://crbug.com/894460.
+    if (variant == "SRC") {
+      libfuzzer_options = [ "close_fd_mask=1" ]
+    }
 
     defines = [ "PIPELINE_FUZZER_VARIANT=${variant}" ]