android/filesystems/ramdisk_extractor.h: new file.

This patch introduces a new function that can be used to
extract single data file content from an Android ramdisk.img
image.

This will be used to extract fstab.goldfish in a future patch
to reliably determine the format of each partition image before
the emulator is run.

Change-Id: I4e8178ce1cedf0e93b852c632003d089bcd41701
diff --git a/Makefile.tests b/Makefile.tests
index b9a5a28..2daabff 100644
--- a/Makefile.tests
+++ b/Makefile.tests
@@ -24,6 +24,7 @@
   android/emulation/CpuAccelerator_unittest.cpp \
   android/filesystems/ext4_utils_unittest.cpp \
   android/filesystems/partition_types_unittest.cpp \
+  android/filesystems/ramdisk_extractor_unittest.cpp \
   android/filesystems/testing/TestSupport.cpp \
   android/kernel/kernel_utils_unittest.cpp \