Fix more disabled MSVC warnings, base/ edition.

base/logging.h

Index: base/logging.h
diff --git a/base/logging.h b/base/logging.h
index 743586492eb615de6fd279a38b0ff2d1d524bf34..4661f0f257ec5a0eaa939f5921877f56eb8dc63d 100644
--- a/base/logging.h
+++ b/base/logging.h
@@ -618,12 +618,12 @@ const LogSeverity LOG_DCHECK = LOG_INFO;
 // variable warnings if the only use of a variable is in a DCHECK.
 // This behavior is different from DLOG_IF et al.
 
-#define DCHECK(condition)                                         \
-  LAZY_STREAM(LOG_STREAM(DCHECK), DCHECK_IS_ON && !(condition))   \
+#define DCHECK(condition)                                               \
+  LAZY_STREAM(LOG_STREAM(DCHECK), DCHECK_IS_ON ? !(condition) : false)  \

[brettw, 2014/10/01 17:54:07]

I don't follow the reason for this change.

[Peter Kasting, 2014/10/01 19:30:21]

My explanatory comment from an earlier patchset (
https://codereview.chromium.org/596103002/diff/1/base/logging.h#newcode622 ):
"This form of the macro eliminates "unused variable" warnings compared to the
other form."

More specifically, since && short-circuits, MSVC doesn't consider the old form
to have "referenced" |condition| as desired when DCHECK_IS_ON is known at
compile time to be false.  Using ?: instead ensures the compiler considers
|condition| to have been referenced in all cases, while preserving the property
that it isn't actually evaluated when DCHECKs are off.

(I ran into these warnings and found a number of helpful pages online noting
that the ?: form was a solution that worked across compilers.)

   << "Check failed: " #condition ". "
 
-#define DPCHECK(condition)                                        \
-  LAZY_STREAM(PLOG_STREAM(DCHECK), DCHECK_IS_ON && !(condition))  \
+#define DPCHECK(condition)                                              \
+  LAZY_STREAM(PLOG_STREAM(DCHECK), DCHECK_IS_ON ? !(condition) : false) \
   << "Check failed: " #condition ". "
 
 // Helper macro for binary operators.