Revert "Remove automatic adding of adb into default.prop"

This reverts commit 3c51c2bc48.

Bug: 32223614
Change-Id: I1addc93b175e9442d9fc2f5e7a557fe818201a27

tools/post_process_props.py

@@ -33,6 +33,16 @@ def mangle_build_prop(prop):
 # Put the modifications that you need to make into the /default.prop into this
 # function. The prop object has get(name) and put(name,value) methods.
 def mangle_default_prop(prop):
+  # If ro.debuggable is 1, then enable adb on USB by default
+  # (this is for userdebug builds)
+  if prop.get("ro.debuggable") == "1":
+    val = prop.get("persist.sys.usb.config")
+    if "adb" not in val:
+      if val == "":
+        val = "adb"
+      else:
+        val = val + ",adb"
+      prop.put("persist.sys.usb.config", val)
   # UsbDeviceManager expects a value here.  If it doesn't get it, it will
   # default to "adb". That might not the right policy there, but it's better
   # to be explicit.