Remove redundant DCHECK_IS_ON() condition in DCHECK_OP() implementation.

The implementation was wrapped with a DCHECK_IS_ON() condition by
https://codereview.chromium.org/2653073002/ but the DCHECK_IS_ON() check
inside the implementation was not removed. Remove it to make the macro
a little easier to read.

Bug: 684105
Change-Id: Ia0e923f89432b31fc2ec32b7438e5e6c416433bf
Reviewed-on: https://chromium-review.googlesource.com/1072455
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#561995}

base/logging.h

@@ -903,9 +903,8 @@ const LogSeverity LOG_DCHECK = LOG_FATAL;
 #define DCHECK_OP(name, op, val1, val2)                                \
   switch (0) case 0: default:                                          \
   if (::logging::CheckOpResult true_if_passed =                        \
-      DCHECK_IS_ON() ?                                                 \
       ::logging::Check##name##Impl((val1), (val2),                     \
-                                   #val1 " " #op " " #val2) : nullptr) \
+                                   #val1 " " #op " " #val2))           \
    ;                                                                   \
   else                                                                 \
     ::logging::LogMessage(__FILE__, __LINE__, ::logging::LOG_DCHECK,   \