polymer.py: Make chrome://resources/ URL rewriting more robust.

Previously the redirects dictionary had to include several
subpaths separately. For example it included the following keys

chrome://resources/polymer/v1_0/
chrome://resources/html/
chrome://resources/cr_elements/

This  was necessary because the redirects where not applied in
any particular order. By turning the dictionary to an OrderedDict
there is no need to hold all these paths, and instead it can only
hold the following

chrome://resources/polymer/v1_0/ (special case redirect)
chrome://resources/              (default redirect)

Which is more robust, and allows correctly redirecting other
non-special subpaths like chrome://resources/cr_components/ without
having to update the dictionary.

Bug: None
Change-Id: I57eb1f0e9241e05a5150b6463410b653fcbf0c60
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2274324Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: dpapad <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#784462}

tools/polymer/polymer.py

@@ -54,6 +54,7 @@ import io
 import os
 import re
 import sys
+from collections import OrderedDict
 
 _CWD = os.getcwd()
 _HERE_PATH = os.path.dirname(__file__)
@@ -78,14 +79,13 @@ _ignore_imports = []
 
 _migrated_imports = []
 
-_chrome_redirects = {
-    'chrome://resources/polymer/v1_0/': POLYMER_V1_DIR,
-    'chrome://resources/html/': 'ui/webui/resources/html/',
-    'chrome://resources/cr_elements/': 'ui/webui/resources/cr_elements/',
-    '//resources/polymer/v1_0/': POLYMER_V1_DIR,
-    '//resources/html/': 'ui/webui/resources/html/',
-    '//resources/cr_elements/': 'ui/webui/resources/cr_elements/',
-}
+# Use an OrderedDict, since the order these redirects are applied matters.
+_chrome_redirects = OrderedDict([
+    ('chrome://resources/polymer/v1_0/', POLYMER_V1_DIR),
+    ('chrome://resources/', 'ui/webui/resources/'),
+    ('//resources/polymer/v1_0/', POLYMER_V1_DIR),
+    ('//resources/', 'ui/webui/resources/'),
+])
 
 _chrome_reverse_redirects = {
     POLYMER_V3_DIR: '//resources/polymer/v3_0/',