Use "crbug.com" instead of "issue" to avoid confusion

Change-Id: I5a5f176793365ee972b0a857531df9daef99ec03
Reviewed-on: https://chromium-review.googlesource.com/c/1343523
Commit-Queue: Xi Cheng <chengx@chromium.org>
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609541}

base/metrics/persistent_histogram_storage_unittest.cc

@@ -50,7 +50,7 @@ class PersistentHistogramStorageTest : public testing::Test {
   DISALLOW_COPY_AND_ASSIGN(PersistentHistogramStorageTest);
 };
 
-// TODO(chengx): Re-enable the test on OS_IOS after issue 836789 is fixed.
+// TODO(chengx): Re-enable the test on OS_IOS after crbug.com/836789 is fixed.
 // PersistentHistogramStorage is only used on OS_WIN now, so disabling this
 // test on OS_IOS is fine.
 #if !defined(OS_NACL) && !defined(OS_IOS)