Switch from WebDocument::insertStyleText to ::insertUserStyleSheet for programatic CSS injection.

chrome/renderer/extensions/user_script_idle_scheduler.cc

Index: chrome/renderer/extensions/user_script_idle_scheduler.cc
diff --git a/chrome/renderer/extensions/user_script_idle_scheduler.cc b/chrome/renderer/extensions/user_script_idle_scheduler.cc
index 827132e5500fec45045f18ddc7d87c3ac4e6f9c7..dc34c4e5d6cea1b12f17c74a0b24b6c8f35c1c45 100644
--- a/chrome/renderer/extensions/user_script_idle_scheduler.cc
+++ b/chrome/renderer/extensions/user_script_idle_scheduler.cc
@@ -23,6 +23,7 @@ namespace {
 const int kUserScriptIdleTimeoutMs = 200;
 }
 
+using WebKit::WebDocument;
 using WebKit::WebFrame;
 using WebKit::WebString;
 using WebKit::WebView;
@@ -151,8 +152,10 @@ void UserScriptIdleScheduler::ExecuteCodeImpl(
             &sources.front(), sources.size(), EXTENSION_GROUP_CONTENT_SCRIPTS);
       }
     } else {
-      frame->document().insertStyleText(
-          WebString::fromUTF8(params.code), WebString());
+      frame->document().insertUserStyleSheet(
+          WebString::fromUTF8(params.code),
+          // Author level is consistent with WebView::addUserStyleSheet.
+          WebDocument::UserStyleAuthorLevel);
     }
   }