Mount system as read-only by default

Mounting system as rw can prevent future OTA updates. The purpose
of this patch set is to prevent TWRP from mounting sytem as rw on
the first boot. Device maintainers should update their twrp.fstab
files on these devices to include an additional line:
/system_image emmc /dev/block/../system

This line will allow TWRP to create a raw system image backup to
ensure that the user can return to an original state for future
OTA updates.

Change-Id: I8929d85bc3a5b96cc564bc7f734b58d5612ec833
diff --git a/partitions.hpp b/partitions.hpp
index f74fac9..1489a8e 100644
--- a/partitions.hpp
+++ b/partitions.hpp
@@ -70,6 +70,8 @@
 	bool Update_Size(bool Display_Error);                                     // Updates size information
 	void Recreate_Media_Folder();                                             // Recreates the /data/media folder
 	bool Flash_Image(string Filename);                                        // Flashes an image to the partition
+	void Change_Mount_Read_Only(bool new_value);                              // Changes Mount_Read_Only to new_value
+	int Check_Lifetime_Writes();
 	string Current_File_System;                                               // Current file system
@@ -167,6 +169,7 @@
 	bool Ignore_Blkid;                                                        // Ignore blkid results due to superblocks lying to us on certain devices / partitions
 	bool Retain_Layout_Version;                                               // Retains the .layout_version file during a wipe (needed on devices like Sony Xperia T where /data and /data/media are separate partitions)
 	bool Can_Flash_Img;                                                       // Indicates if this partition can have images flashed to it via the GUI
+	bool Mount_Read_Only;                                                     // Only mount this partition as read-only
 friend class TWPartitionManager;
 friend class DataManager;