Open Radar

 
Summary:
The `-[XCTestCase measureBlock:]` and `-[XCTestCase measureMetrics:automaticallyStartMeasuring:forBlock:]` methods each take blocks for which `noescape` semantics apply. That is, no reference to the block parameters remains once the methods return. Adding the `__attribute__((noescape))` annotation to these parameters would make this fact explicit, and allow the Swift importer to mark the params as `@noescape` in Swift, which in turn would remove the need to explicitly reference `self` when using members within the blocks.

Specifically, it is currently necessary to fully spell out `self.startMeasuring()` and `self.stopMeasuring()`, like this:

```
measureMetrics([XCTPerformanceMetric_WallClockTime], automaticallyStartMeasuring: false) {
    self.startMeasuring()
    // Do work
    self.stopMeasuring()
}
```

With the added annotation, it can be simplified like this:

```
measureMetrics([XCTPerformanceMetric_WallClockTime], automaticallyStartMeasuring: false) {
    startMeasuring()
    // Do work
    stopMeasuring()
}
```