applypatch: Support flash mode.

We may carry a full copy of recovery image in the /system, and use
/system/bin/install-recovery.sh to install the recovery. This CL adds
support to flash the recovery partition with the given image.

Bug: 22641135
Change-Id: I7a275b62fdd1bf41f97f6aab62d0200f7dae5aa1
(cherry picked from commit 68c5a6796737bb583a8bdfa4c9cd9c7f12ef4276)
diff --git a/applypatch/applypatch.h b/applypatch/applypatch.h
index edec848..415bc1b 100644
--- a/applypatch/applypatch.h
+++ b/applypatch/applypatch.h
@@ -48,6 +48,8 @@
 int CacheSizeCheck(size_t bytes);
 int ParseSha1(const char* str, uint8_t* digest);
 
+int applypatch_flash(const char* source_filename, const char* target_filename,
+                     const char* target_sha1_str, size_t target_size);
 int applypatch(const char* source_filename,
                const char* target_filename,
                const char* target_sha1_str,