Get Wheel entrypoints from Distribution instead of file

Since the Distribution pulls its data directly from the Wheel file,
without extracting intermediate files to disk, this brings us closer to
installing from Wheels without extracting everything.

src/pip/_internal/operations/install/wheel.py

@@ -7,7 +7,6 @@ import collections
 import compileall
 import contextlib
 import csv
-import io
 import logging
 import os.path
 import re
@@ -124,16 +123,14 @@ def wheel_root_is_purelib(metadata):
 
 def get_entrypoints(filename, distribution):
     # type: (str, Distribution) -> Tuple[Dict[str, str], Dict[str, str]]
-    if not os.path.exists(filename):
-        return {}, {}
-
-    with io.open(filename, encoding="utf-8") as fp:
-        data = fp.read()
-
     # get the entry points and then the script names
-    entry_points = pkg_resources.EntryPoint.parse_map(data)
-    console = entry_points.get('console_scripts', {})
-    gui = entry_points.get('gui_scripts', {})
+    try:
+        console = distribution.get_entry_map('console_scripts')
+        gui = distribution.get_entry_map('gui_scripts')
+    except KeyError:
+        # Our dict-based Distribution raises KeyError if entry_points.txt
+        # doesn't exist.
+        return {}, {}
 
     def _split_ep(s):
         # type: (pkg_resources.EntryPoint) -> Tuple[str, str]