Make the log message in setInteractive a local variable.

If the error message isn't a local variable, it will go out of scope
immediately after LogIfSlow is constructed. Unfortunately, LogIfSlow
maintains a pointer to String8s internal char* member... which causes a
use after free when it goes to log. Oops.

Bug: 62820330
Test: none
Change-Id: Ie1da3be723f8aae165822002ff42954480a43aa5