Add DwarfMemory class.

Bug: 23762183

Test: Passes new unit tests.
Change-Id: I80293af0b5a8a042195c37a06d64082d2f7c781a
diff --git a/libunwindstack/Android.bp b/libunwindstack/Android.bp
index ece623b..dabeac1 100644
--- a/libunwindstack/Android.bp
+++ b/libunwindstack/Android.bp
@@ -47,6 +47,7 @@
 
     srcs: [
         "ArmExidx.cpp",
+        "DwarfMemory.cpp",
         "Elf.cpp",
         "ElfInterface.cpp",
         "ElfInterfaceArm.cpp",
@@ -87,6 +88,7 @@
     srcs: [
         "tests/ArmExidxDecodeTest.cpp",
         "tests/ArmExidxExtractTest.cpp",
+        "tests/DwarfMemoryTest.cpp",
         "tests/ElfInterfaceArmTest.cpp",
         "tests/ElfInterfaceTest.cpp",
         "tests/ElfTest.cpp",