Update from https://crrev.com/311076

base/files/memory_mapped_file_posix.cc

Index: base/files/memory_mapped_file_posix.cc
diff --git a/base/files/memory_mapped_file_posix.cc b/base/files/memory_mapped_file_posix.cc
index ebf38779f039708835242eb19ed7223927a28f40..168da923d469641cd7b17d80c7f10b53e67ada5b 100644
--- a/base/files/memory_mapped_file_posix.cc
+++ b/base/files/memory_mapped_file_posix.cc
@@ -16,6 +16,7 @@ namespace base {
 MemoryMappedFile::MemoryMappedFile() : data_(NULL), length_(0) {
 }
 
+#if !defined(OS_NACL)
 bool MemoryMappedFile::MapFileRegionToMemory(
     const MemoryMappedFile::Region& region) {
   ThreadRestrictions::AssertIOAllowed();
@@ -74,6 +75,7 @@ bool MemoryMappedFile::MapFileRegionToMemory(
   data_ += data_offset;
   return true;
 }
+#endif
 
 void MemoryMappedFile::CloseHandles() {
   ThreadRestrictions::AssertIOAllowed();