Teach i18nTemplate.process() to handle <link rel=import> and <template>

ui/webui/resources/css/i18n_process.css

Index: ui/webui/resources/css/i18n_process.css
diff --git a/ui/webui/resources/css/i18n_process.css b/ui/webui/resources/css/i18n_process.css
index 44ca4b2ed20de5e2d8449cbbc925778f2d39bdf8..b74527a08f2c9f34c6dc6e0b406070eaa531d537 100644
--- a/ui/webui/resources/css/i18n_process.css
+++ b/ui/webui/resources/css/i18n_process.css
@@ -2,8 +2,16 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file. */
 
-html:not(.i18n-processed) [i18n-content]::before,
-html:not(.i18n-processed) [i18n-values*=".innerHTML:"]::before {
+[i18n-content]::before,
+[i18n-values*=".innerHTML:"]::before {
   /* Insert a non-breaking space into nodes that have i18n'd content. */
   content: '\00a0';
 }
+
+[i18n-processed][i18n-content]::before,
+[i18n-processed] [i18n-content]::before,
+[i18n-processed][i18n-values*=".innerHTML:"]::before,
+[i18n-processed] [i18n-values*=".innerHTML:"]::before {
+  /* Undo the non-breaking space hack after i18n-processing has run. */
+  content: normal;
+}