Update from https://crrev.com/311076

base/posix/global_descriptors.h

Index: base/posix/global_descriptors.h
diff --git a/base/posix/global_descriptors.h b/base/posix/global_descriptors.h
index 3d7369c3174a9e8f0df4b0cdd85c4428111a94db..c774634f59bf9c45bd9acce2a7762de19b3b257b 100644
--- a/base/posix/global_descriptors.h
+++ b/base/posix/global_descriptors.h
@@ -12,6 +12,7 @@
 
 #include <stdint.h>
 
+#include "base/files/memory_mapped_file.h"
 #include "base/memory/singleton.h"
 
 namespace base {
@@ -36,8 +37,18 @@ namespace base {
 class BASE_EXPORT GlobalDescriptors {
  public:
   typedef uint32_t Key;
-  typedef std::pair<Key, int> KeyFDPair;
-  typedef std::vector<KeyFDPair> Mapping;
+  struct Descriptor {
+    Descriptor(Key key, int fd);
+    Descriptor(Key key, int fd, base::MemoryMappedFile::Region region);
+
+    // Globally unique key.
+    Key key;
+    // Actual FD.
+    int fd;
+    // Optional region, defaults to kWholeFile.
+    base::MemoryMappedFile::Region region;
+  };
+  typedef std::vector<Descriptor> Mapping;
 
   // Often we want a canonical descriptor for a given Key. In this case, we add
   // the following constant to the key value:
@@ -53,12 +64,19 @@ class BASE_EXPORT GlobalDescriptors {
   // Get a descriptor given a key. It is a fatal error if the key is not known.
   int Get(Key key) const;
 
-  // Get a descriptor give a key. Returns -1 on error.
+  // Get a descriptor given a key. Returns -1 on error.
   int MaybeGet(Key key) const;
 
-  // Set the descriptor for the given key.
+  // Get a region given a key. It is a fatal error if the key is not known.
+  base::MemoryMappedFile::Region GetRegion(Key key) const;
+
+  // Set the descriptor for the given |key|. This sets the region associated
+  // with |key| to kWholeFile.
   void Set(Key key, int fd);
 
+  // Set the descriptor and |region| for the given |key|.
+  void Set(Key key, int fd, base::MemoryMappedFile::Region region);
+
   void Reset(const Mapping& mapping);
 
  private: