base: Avoid compilation error when compiled with -Wdangling-else.

As logging macros uses `if xxx else yyy` style, it is reported as an
error when DCHECK() is compiled with -Wdangling-else option. Because
after preprocess, DCHECK(x) becomes:
if (EnableDChecks)
  if (x)
    ;
  else
    LogMessage(FATAL) << yyy;

This CL avoids compilation error by replacing `if xxx else yyy`
with `xxx && yyy` or `!(xxx) || yyy`.

Bug: 26962895

Change-Id: Ib0bf242cc04a238ec31a1ab66b53fc8a5b5ed28f