Reland 'Convert //net and //chromecast to std::unordered_*'

net/base/platform_mime_util.h

Index: net/base/platform_mime_util.h
diff --git a/net/base/platform_mime_util.h b/net/base/platform_mime_util.h
index 726cea4341458f3bce057753bac50dbc33443f4a..f79d84324a9df2539ef3e62080f3c63924d78cd4 100644
--- a/net/base/platform_mime_util.h
+++ b/net/base/platform_mime_util.h
@@ -6,8 +6,8 @@
 #define NET_BASE_PLATFORM_MIME_UTIL_H_
 
 #include <string>
+#include <unordered_set>
 
-#include "base/containers/hash_tables.h"
 #include "base/files/file_path.h"
 
 namespace net {
@@ -25,7 +25,7 @@ class PlatformMimeUtil {
   // by GetPreferredExtensionForMimeType.
   void GetPlatformExtensionsForMimeType(
       const std::string& mime_type,
-      base::hash_set<base::FilePath::StringType>* extensions) const;
+      std::unordered_set<base::FilePath::StringType>* extensions) const;
 
  protected:
   // Get the mime type (if any) that is associated with the file extension.