ART: Track Flush & Close in FdFile

Implement a check that aborts when a file hasn't been explicitly
flushed and closed when it is destructed.

Add WARN_UNUSED to FdFile methods.

Update dex2oat, patchoat, scoped_flock and some gtests to pass with
this.

(cherry picked from commit 9433ec60b325b708b9fa87e699ab4a6565741494)

Change-Id: I9ab03b1653e69f44cc98946dc89d764c3e045dd4
diff --git a/oatdump/oatdump.cc b/oatdump/oatdump.cc
index d6309f7..ea71996 100644
--- a/oatdump/oatdump.cc
+++ b/oatdump/oatdump.cc
@@ -182,8 +182,8 @@
 
     bool result = builder_->Write();
 
-    elf_output_->Flush();
-    elf_output_->Close();
+    // Ignore I/O errors.
+    UNUSED(elf_output_->FlushClose());
 
     return result;
   }