Work around /analyze internal compiler error

VS 2015 Update 3 fixes one internal compiler error, but hits another one
when compiling Chrome. This CL works around the new internal compiler
error by avoiding using a DCHECK (which uses __analysis_assume, which
triggers the problem) when compiling for /analyze. _PREFAST_ is defined
for all /analyze compiles.

BUG=427616

Review-Url: https://codereview.chromium.org/2104893004
Cr-Commit-Position: refs/heads/master@{#402910}
1 file changed