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/ElfInterfaceArm.h b/libunwindstack/ElfInterfaceArm.h
index eeb2e17..9c067ba 100644
--- a/libunwindstack/ElfInterfaceArm.h
+++ b/libunwindstack/ElfInterfaceArm.h
@@ -70,9 +70,11 @@
 
   bool HandleType(uint64_t offset, uint32_t type, uint64_t load_bias) override;
 
-  bool Step(uint64_t pc, Regs* regs, Memory* process_memory, bool* finished) override;
+  bool Step(uint64_t pc, uint64_t load_bias, Regs* regs, Memory* process_memory,
+            bool* finished) override;
 
-  bool StepExidx(uint64_t pc, Regs* regs, Memory* process_memory, bool* finished);
+  bool StepExidx(uint64_t pc, uint64_t load_bias, Regs* regs, Memory* process_memory,
+                 bool* finished);
 
   uint64_t start_offset() { return start_offset_; }