Probably not. The compiler optimizes for size over speed. Looking at the compiler output, I see that `goog.isString` becomes:
```javascript
function la(a){return"string"==typeof a}
```
So, instead of inlining (which would produce `"typeof x=='string'".length` == 18 bytes per call), it uses `la(x)` which is just 4 bytes per call. Note that `goog.isString` is used throughout the codebase.