Appease buildbots after r280114.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280117 91177308-0d34-0410-b5e6-96231b3b80d8

Author: Zachary Turner

include/llvm/ADT/ArrayRef.h

@@ -342,15 +342,15 @@ namespace llvm {
     MutableArrayRef<T> keep_front(size_t N = 1) const {
       if (N >= this->size())
         return *this;
-      return drop_back(size() - N);
+      return drop_back(this->size() - N);
     }
 
     /// \brief Drop everything but the last \p N elements of the array.
     LLVM_ATTRIBUTE_UNUSED_RESULT
     MutableArrayRef<T> keep_back(size_t N = 1) const {
       if (N >= this->size())
         return *this;
-      return drop_front(size() - N);
+      return drop_front(this->size() - N);
     }
 
     /// @}