Flaky coverage/package:front_end/src/fasta/type_inference/inference_visitor_base.dart on front-end-linux-release-x64-try

[alexmarkov]

While running CQ on a change which doesn't touch front-end sources, I got the following failure on front-end-linux-release-x64-try bot:

/=====================================================================================================================\
| coverage/package:front_end/src/fasta/type_inference/inference_visitor_base.dart broke (Pass -> Fail, expected Pass) |
\=====================================================================================================================/

package:front_end/src/fasta/type_inference/inference_visitor_base.dart: 84% (448 misses)
package:front_end/src/fasta/type_inference/inference_visitor_base.dart:187: No coverage for 'InferenceVisitorBase.staticTypeContext'.
  StaticTypeContext get staticTypeContext => _inferrer.staticTypeContext;

...

Expected at least 84%, got 83.95415472779369% (2344 hits and 448 misses).

To re-run this test, run:

   dart --enable-asserts pkg/front_end/test/coverage_suite.dart --tasks=5

Log: https://logs.chromium.org/logs/dart/buildbucket/cr-buildbucket/8745765627014184241/+/u/test_results/new_test_failures__logs_

Re-running try-job was successful, so the failure is flaky.

/cc @johnniwinther @jensjoha