Reland r50057. This is exactly the same except with two lines cherrypicked from

app/resource_bundle.h

Index: app/resource_bundle.h
diff --git a/app/resource_bundle.h b/app/resource_bundle.h
index 3a3e617bfa697735e6c1e84330a39792fc283ca2..1d328a34f461f0b508c2abb3ed5d83112d9b0c6d 100644
--- a/app/resource_bundle.h
+++ b/app/resource_bundle.h
@@ -159,8 +159,9 @@ class ResourceBundle {
   // Helper class for managing data packs.
   class LoadedDataPack {
    public:
-    LoadedDataPack(const FilePath& path);
-    bool GetStringPiece(int resource_id, base::StringPiece* data);
+    explicit LoadedDataPack(const FilePath& path);
+    bool GetStringPiece(int resource_id, base::StringPiece* data) const;
+    RefCountedStaticMemory* GetStaticMemory(int resource_id) const;
 
    private:
     void Load();