Dump dex file sizes in oatdump.

Change-Id: I15d1ecfb9900a07b36209015e8b47718fdee19a7
diff --git a/src/oat_file.cc b/src/oat_file.cc
index 1e9d820..4e05325 100644
--- a/src/oat_file.cc
+++ b/src/oat_file.cc
@@ -234,9 +234,12 @@
 
 OatFile::OatDexFile::~OatDexFile() {}
 
+size_t OatFile::OatDexFile::FileSize() const {
+  return reinterpret_cast<const DexFile::Header*>(dex_file_pointer_)->file_size_;
+}
+
 const DexFile* OatFile::OatDexFile::OpenDexFile() const {
-  size_t length = reinterpret_cast<const DexFile::Header*>(dex_file_pointer_)->file_size_;
-  return DexFile::Open(dex_file_pointer_, length, dex_file_location_,
+  return DexFile::Open(dex_file_pointer_, FileSize(), dex_file_location_,
                        dex_file_location_checksum_);
 }