[cros, user_manager] Move default user images constants and helper functions out of src/chrome.

chrome/chrome_browser.gypi

Index: chrome/chrome_browser.gypi
diff --git a/chrome/chrome_browser.gypi b/chrome/chrome_browser.gypi
index a52f072aaae408745114af56ebd32827401181de..641db2c5107d8e1e558d84342e0a0466c5f80dbc 100644
--- a/chrome/chrome_browser.gypi
+++ b/chrome/chrome_browser.gypi
@@ -3378,6 +3378,13 @@
         }],
         ['enable_managed_users==1', {
           'sources': [ '<@(chrome_browser_supervised_user_sources)' ],
+          'conditions' : [
+            [ 'chromeos==1', {
+              'dependencies': [
+                '<(DEPTH)/components/components.gyp:user_manager',
+              ]
+            }]
+          ]
         }],
         ['enable_webrtc==1', {
           'sources': [ '<@(chrome_browser_webrtc_sources)' ]