Re-enable libunwind for arm.

Update to handle the new optimized way that libunwind works.

In addition, a small refactor of the BacktraceMap code.

A few new tests of for good measure.

Change-Id: I2f9b4f5ad5a0dfe907b31febee76e4b9b94fb76f
diff --git a/libbacktrace/UnwindMap.h b/libbacktrace/UnwindMap.h
new file mode 100644
index 0000000..5a874e8
--- /dev/null
+++ b/libbacktrace/UnwindMap.h
@@ -0,0 +1,39 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _LIBBACKTRACE_UNWIND_MAP_H
+#define _LIBBACKTRACE_UNWIND_MAP_H
+
+#include <backtrace/BacktraceMap.h>
+
+// The unw_map_cursor_t structure is different depending on whether it is
+// the local or remote version. In order to get the correct version, include
+// libunwind.h first then this header.
+
+class UnwindMap : public BacktraceMap {
+public:
+  UnwindMap(pid_t pid);
+  virtual ~UnwindMap();
+
+  virtual bool Build();
+
+  unw_map_cursor_t* GetMapCursor() { return &map_cursor_; }
+
+private:
+  unw_map_cursor_t map_cursor_;
+};
+
+#endif // _LIBBACKTRACE_UNWIND_MAP_H