Fix a leak in Parcel::writeBlob.

Was mistakenly assuming that Parcel::writeFileDescriptor took
ownership of the fd that was passed in.  It does not!
Added some comments and a default parameter to allow the caller
to specify whether it wishes the Parcel to take ownership.

Bug: 5563374
Change-Id: I5a12f51d582bf246ce90133cce7690bb9bca93f6
diff --git a/include/binder/Parcel.h b/include/binder/Parcel.h
index 3fa2acb..33b2f00 100644
--- a/include/binder/Parcel.h
+++ b/include/binder/Parcel.h
@@ -110,7 +110,8 @@
     
     // Place a file descriptor into the parcel.  The given fd must remain
     // valid for the lifetime of the parcel.
-    status_t            writeFileDescriptor(int fd);
+    // The Parcel does not take ownership of the given fd unless you ask it to.
+    status_t            writeFileDescriptor(int fd, bool takeOwnership = false);
     
     // Place a file descriptor into the parcel.  A dup of the fd is made, which
     // will be closed once the parcel is destroyed.