[Sheriff] Disable DiskCacheTest.BlockFiles_Grow on ChromeOS

Test is flaking heavily on chromeos-amd64-generic-rel

Bug: 1156795

TBR=jkarlin@chromium.org

Change-Id: I8f627f24f01654fe2845aad2cc7629365d9b77fb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2595589Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837611}

net/disk_cache/blockfile/block_files_unittest.cc

@@ -29,7 +29,13 @@ int NumberOfFiles(const base::FilePath& path) {
 
 namespace disk_cache {
 
-TEST_F(DiskCacheTest, BlockFiles_Grow) {
+// Flaky on ChromeOS: https://crbug.com/1156795
+#if defined(OS_CHROMEOS)
+#define MAYBE_BlockFiles_Grow DISABLED_BlockFiles_Grow
+#else
+#define MAYBE_BlockFiles_Grow BlockFiles_Grow
+#endif
+TEST_F(DiskCacheTest, MAYBE_BlockFiles_Grow) {
   ASSERT_TRUE(CleanupCacheDir());
   ASSERT_TRUE(base::CreateDirectory(cache_path_));