Disable flaky FilenameUtilTest.GenerateSafeFileName test

TBR=asanka@chromium.org

Bug: 828954
Change-Id: Ifb43987ec0e7e892e6655d4f1469b57daae50be6
Reviewed-on: https://chromium-review.googlesource.com/997055Reviewed-by: Darren Shen <shend@chromium.org>
Commit-Queue: Darren Shen <shend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548335}

net/base/filename_util_unittest.cc

@@ -284,7 +284,8 @@ TEST(FilenameUtilTest, FileURLConversion) {
   EXPECT_FALSE(FileURLToFilePath(GURL("filefoobar"), &output));
 }
 
-TEST(FilenameUtilTest, GenerateSafeFileName) {
+// Flaky, see http://crbug.com/828954.
+TEST(FilenameUtilTest, DISABLED_GenerateSafeFileName) {
   const struct {
     const char* mime_type;
     const base::FilePath::CharType* filename;