Extract external file systems handling from isolated context.

webkit/fileapi/file_system_context.h

Index: webkit/fileapi/file_system_context.h
diff --git a/webkit/fileapi/file_system_context.h b/webkit/fileapi/file_system_context.h
index e71fe73f0c8deb3ec5c44836d9f74c9af58f0ca3..9704f20e4575a559faf67c1f10f9eab360d9bbe5 100644
--- a/webkit/fileapi/file_system_context.h
+++ b/webkit/fileapi/file_system_context.h
@@ -19,6 +19,10 @@
 
 class FilePath;
 
+namespace fileapi {
+class ExternalMountPoints;
+}
+
 namespace quota {
 class QuotaManagerProxy;
 class SpecialStoragePolicy;
@@ -201,6 +205,9 @@ class WEBKIT_STORAGE_EXPORT FileSystemContext
   // The base path of the storage partition for this context.
   const FilePath partition_path_;
 
+  // External mount points specific to the context.
+  scoped_refptr<fileapi::ExternalMountPoints> external_mount_points_;
+
   // For syncable file systems.
   scoped_ptr<LocalFileChangeTracker> change_tracker_;
   scoped_refptr<LocalFileSyncContext> sync_context_;