Fix issues in libunwindstack.

- Add a load_bias field in MapInfo so that it can be loaded offline,
  and also so it can be cached.
- Add an Add function to the Maps class so that it's possible to manually
  create a map.
- Remove the OfflineMaps class since I haven't found a reason for this to
  exist.
- Add a pointer to the gnu debugdata compressed section in the interface
  itself and modify the step path to try eh_frame, then debug_frame, then
  gnu_debugdata. This way arm can add exidx as the last step behind
  gnu_debugdata. Add an offline test to verify the order of unwind.
- Fix x86_64_ucontext_t since it was a different size on 32 bit and 64 bit
  systems.

Test: Pass new unit tests.
Change-Id: I978b70d6c244bd307c62a29886d24c1a8cb2af23
diff --git a/libunwindstack/tests/MapsTest.cpp b/libunwindstack/tests/MapsTest.cpp
index 8dc884f..9622ba5 100644
--- a/libunwindstack/tests/MapsTest.cpp
+++ b/libunwindstack/tests/MapsTest.cpp
@@ -44,6 +44,24 @@
   }
 }
 
+TEST(MapsTest, map_add) {
+  Maps maps;
+
+  maps.Add(0x1000, 0x2000, 0, PROT_READ, "fake_map", 0);
+  maps.Add(0x3000, 0x4000, 0x10, 0, "", 0x1234);
+  maps.Add(0x5000, 0x6000, 1, 2, "fake_map2", static_cast<uint64_t>(-1));
+
+  ASSERT_EQ(3U, maps.Total());
+  MapInfo* info = maps.Get(0);
+  ASSERT_EQ(0x1000U, info->start);
+  ASSERT_EQ(0x2000U, info->end);
+  ASSERT_EQ(0U, info->offset);
+  ASSERT_EQ(PROT_READ, info->flags);
+  ASSERT_EQ("fake_map", info->name);
+  ASSERT_EQ(0U, info->elf_offset);
+  ASSERT_EQ(0U, info->load_bias.load());
+}
+
 TEST(MapsTest, verify_parse_line) {
   MapInfo info;