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

net/base/platform_mime_util_linux.cc

Index: net/base/platform_mime_util_linux.cc
diff --git a/net/base/platform_mime_util_linux.cc b/net/base/platform_mime_util_linux.cc
index 13af8f80f68d2afebfa560fa3863b6f1245c3463..7d0fa1ef28753ef719600397c58b96219fec99eb 100644
--- a/net/base/platform_mime_util_linux.cc
+++ b/net/base/platform_mime_util_linux.cc
@@ -102,7 +102,7 @@ bool PlatformMimeUtil::GetPreferredExtensionForMimeType(
 
 void PlatformMimeUtil::GetPlatformExtensionsForMimeType(
     const std::string& mime_type,
-    base::hash_set<base::FilePath::StringType>* extensions) const {
+    std::unordered_set<base::FilePath::StringType>* extensions) const {
   base::FilePath::StringType ext;
   if (GetPreferredExtensionForMimeType(mime_type, &ext))
     extensions->insert(ext);