Fix small issues in prefix positioning.

parso/python/prefix.py

@@ -11,9 +11,9 @@ class PrefixToken(object):
 
     @property
     def end_pos(self):
-        if '\n' in self.value:
+        if self.value.endswith('\n'):
             return self.start_pos[0] + 1, 0
-        return self.end_pos[1]
+        return self.start_pos[0], self.start_pos[1] + len(self.value)
 
 
 _comment = r'#[^\n\r\f]*'
@@ -46,6 +46,6 @@ def split_prefix(prefix, start_pos):
         yield PrefixToken(typ, value, (line, column + start))
 
         start = match.end(0)
-        if '\n' in value:
+        if value.endswith('\n'):
             line += 1
             column = -start

parso/python/tree.py

@@ -101,7 +101,7 @@ class PythonLeaf(PythonMixin, Leaf):
     __slots__ = ()
 
     def _split_prefix(self):
-        return split_prefix(self.prefix, self.start_pos)
+        return split_prefix(self.prefix, self.get_start_pos_of_prefix())
 
 
 class _LeafWithoutNewlines(PythonLeaf):

test/test_prefix.py

@@ -20,8 +20,21 @@ def test_simple_prefix_splitting(string, tokens):
     tree = parso.parse(string)
     leaf = tree.children[0]
     assert leaf.type == 'endmarker'
+
     parsed_tokens = list(leaf._split_prefix())
-    assert [t.value for t in parsed_tokens] == tokens
+    start_pos = (1, 0)
+    for pt, expected in zip(parsed_tokens, tokens):
+        assert pt.value == expected
+
+        # Calculate the estimated end_pos
+        if expected.endswith('\n'):
+            end_pos = start_pos[0] + 1, 0
+        else:
+            end_pos = start_pos[0], start_pos[1] + len(expected)
+
+        #assert start_pos == pt.start_pos
+        assert end_pos == pt.end_pos
+        start_pos = end_pos
 
 
 @pytest.mark.parametrize(('string', 'types'), [