type_tostring_test and nested_generic_closure_test failing after ac41a200

[sjindel-google]

See https://ci.chromium.org/p/dart/builders/ci.sandbox/vm-dartkb-linux-product-x64/982 for example.

The failures have been seen on vm-dartkb-linux-product-simarm64 and vm-dartkb-linux-product-x64 so far.

[sjindel-google]

It's also appeared on the obfuscation bot, although with a different error.

[alexmarkov]

Dartkb failures indicate the real bugs, revealed by newly added tests. I'll take a look at them.

Regarding obfuscation bot: we can either skip corelib_2/type_tostring_test on the obfuscation bot, or add @pragma("vm:entry-point") annotations to prevent obfuscation of names used in the test.

[crelier]

I also approved these failures showing on vm-dartkb-linux-debug-x64 and vm-dartkb-linux-debug-simarm64.