Analyzer detection of block-bodied functions in type inference is incomplete.

[stereotype441]

The analyzer contains a hint, TOP_LEVEL_FUNCTION_LITERAL_BLOCK, to let the user know that type inference results may not be reliable due to the appearance of a block-bodied function in a variable's initializer. (The common front end can type infer such variables accurately; the analyzer can't always).

Unfortunately, this hint does not always fire correctly. For example, the following code currently should produce the hint, but it doesn't:

T f<T>(T Function() g) => g();
var y = f(() { return 0; });

I'm working on a fix.