gn2bp: some functions should fail silently

It is helpful to have certain functions that deal with target.args fail
silently if the arg does not exist. This eliminates the need to
specifically check for the arg's existence.

Test: none
Change-Id: Ia424a25d0b910c9c0de73d3cefbae21cce598ca9

tools/gn2bp/gen_android_bp

@@ -652,17 +652,26 @@ class BaseActionSanitizer():
     return self.target.args[i + 1]
 
   def _set_value_arg(self, arg, value):
+    # Fail silently
+    if not self._has_arg(arg):
+      return
     assert(self._is_value_arg(arg))
     i = self.target.args.index(arg)
     self.target.args[i + 1] = value
 
   def _update_value_arg(self, arg, func):
+    # Fail silently
+    if not self._has_arg(arg):
+      return
     self._set_value_arg(arg, func(self._get_value_arg(arg)))
 
   def _set_arg_at(self, position, value):
     self.target.args[position] = value
 
   def _delete_arg(self, arg):
+    # Fail silently
+    if not self._has_arg(arg):
+      return
     assert(not self._is_list_arg(arg))
     hasValue = self._is_value_arg(arg)
     i = self.target.index(arg)
@@ -705,7 +714,6 @@ class JniGeneratorSanitizer(BaseActionSanitizer):
   def get_args(self):
     if self._has_arg('--jar_file'):
       self._append_arg('--javap', '$$(find out/.path -name javap)')
-    if self._has_arg('--output_dir'):
     self._update_value_arg('--output_dir', self._sanitize_dir)
     return super().get_args()