base: Add CHECK_IMPLIES and DCHECK_IMPLIES.

base/logging.h

Index: base/logging.h
diff --git a/base/logging.h b/base/logging.h
index 743586492eb615de6fd279a38b0ff2d1d524bf34..33bfbc76c9b5a4309b67c00e5bdb518541ab680c 100644
--- a/base/logging.h
+++ b/base/logging.h
@@ -532,6 +532,7 @@ DEFINE_CHECK_OP_IMPL(GT, > )
 #define CHECK_LT(val1, val2) CHECK_OP(LT, < , val1, val2)
 #define CHECK_GE(val1, val2) CHECK_OP(GE, >=, val1, val2)
 #define CHECK_GT(val1, val2) CHECK_OP(GT, > , val1, val2)
+#define CHECK_IMPLIES(val1, val2) CHECK(!(val1) || (val2))
 
 #if defined(NDEBUG)
 #define ENABLE_DLOG 0
@@ -662,6 +663,7 @@ const LogSeverity LOG_DCHECK = LOG_INFO;
 #define DCHECK_LT(val1, val2) DCHECK_OP(LT, < , val1, val2)
 #define DCHECK_GE(val1, val2) DCHECK_OP(GE, >=, val1, val2)
 #define DCHECK_GT(val1, val2) DCHECK_OP(GT, > , val1, val2)
+#define DCHECK_IMPLIES(val1, val2) DCHECK(!(val1) || (val2))
 
 #if defined(NDEBUG) && defined(OS_CHROMEOS)
 #define NOTREACHED() LOG(ERROR) << "NOTREACHED() hit in " << \