Fix setting of map_offset in frame data.

The old code set the map_offset from elf_offset, but it should have used
offset. Without this change, frame data is not properly shown for shared
libraries in an apk.

Add new unit test to verify that map_offset is set properly.

Test: Ran new unit tests.
Change-Id: I2fe5abda23a5de51c8fcf9361ba9350b80446f15
diff --git a/libunwindstack/Unwinder.cpp b/libunwindstack/Unwinder.cpp
index e648927..15a8893 100644
--- a/libunwindstack/Unwinder.cpp
+++ b/libunwindstack/Unwinder.cpp
@@ -52,7 +52,7 @@
   }
 
   frame->map_name = map_info->name;
-  frame->map_offset = map_info->elf_offset;
+  frame->map_offset = map_info->offset;
   frame->map_start = map_info->start;
   frame->map_end = map_info->end;
   frame->map_flags = map_info->flags;