Convert i18n_process.css to use /deep/ instead of ::shadow and add tests.

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 ee92c6027896056053e89b8b7ee937d20b7dcee4..fce3833d79bae32a50961dc553c01599ccb71e0c 100644
--- a/ui/webui/resources/css/i18n_process.css
+++ b/ui/webui/resources/css/i18n_process.css
@@ -4,8 +4,8 @@
 
 [i18n-content]::before,
 [i18n-values*=".innerHTML:"]::before,
-::shadow [i18n-content]::before,
-::shadow [i18n-values*=".innerHTML:"]::before {
+* /deep/ [i18n-content]::before,
+* /deep/ [i18n-values*=".innerHTML:"]::before {
   /* Insert a non-breaking space into nodes that have i18n content. */
   content: '\00a0';
 }
@@ -14,10 +14,10 @@
 [i18n-processed] [i18n-content]::before,
 [i18n-processed][i18n-values*=".innerHTML:"]::before,
 [i18n-processed] [i18n-values*=".innerHTML:"]::before,
-::shadow [i18n-processed][i18n-content]::before,
-::shadow [i18n-processed] [i18n-content]::before,
-::shadow [i18n-processed][i18n-values*=".innerHTML:"]::before,
-::shadow [i18n-processed] [i18n-values*=".innerHTML:"]::before {
+* /deep/ [i18n-processed][i18n-content]::before,
+* /deep/ [i18n-processed] [i18n-content]::before,
+* /deep/ [i18n-processed][i18n-values*=".innerHTML:"]::before,
+* /deep/ [i18n-processed] [i18n-values*=".innerHTML:"]::before {
   /* Undo the non-breaking space hack after i18n processing has run. */
   content: normal;

[esprehn, 2015/07/21 23:42:02]

This is pretty bad for performance, what's this code trying to do?

[Dan Beam, 2015/07/22 00:15:40]

not flicker as bad when the whole page changes its content
https://codereview.chromium.org/1076093002

 }