Add new user script injection point: document_idle.

chrome/common/extensions/user_script.h

Index: chrome/common/extensions/user_script.h
diff --git a/chrome/common/extensions/user_script.h b/chrome/common/extensions/user_script.h
index 28b3aaec1928117c1bcda7f21f49eb41a688ddf0..bdd1e5435fdd7f201eee32617192cf5195af2c22 100644
--- a/chrome/common/extensions/user_script.h
+++ b/chrome/common/extensions/user_script.h
@@ -28,6 +28,10 @@ class UserScript {
                      // anything else happens.
     DOCUMENT_END,  // After the entire document is parsed. Same as
                    // DOMContentLoaded.
+    DOCUMENT_IDLE,  // Sometime after DOMContentLoaded, as soon as the document
+                    // is "idle". Currently this uses the simple heuristic of:
+                    // min(DOM_CONTENT_LOADED + TIMEOUT, ONLOAD), but no
+                    // particular injection point is guaranteed.
 
     RUN_LOCATION_LAST  // Leave this as the last item.
   };
@@ -88,9 +92,10 @@ class UserScript {
 
   typedef std::vector<File> FileList;
 
-  // Constructor. Default the run location to document end, which is like
-  // Greasemonkey and probably more useful for typical scripts.
-  UserScript() : run_location_(DOCUMENT_END) {}
+  // Constructor. Default the run location to document idle, which is similar
+  // to Greasemonkey but should result in better page load times for fast-
+  // loading pages.
+  UserScript() : run_location_(DOCUMENT_IDLE) {}
 
   // The place in the document to run the script.
   RunLocation run_location() const { return run_location_; }