CloseGuard: Fix JavaDoc code sample to use correct API

The code sample in the JavaDoc shows
`CloseGuard.get()` to create a new CloseGuard,
which is incorrect.
The correct API is `new CloseGuard()`.

Bug: 148291235
Test: compiles
Change-Id: I1dd24fff150e671007b67c023b20e078557f2966
1 file changed