[ChromeDriver] Send DOM.getDocument after each DOM.documentUpdated.

chrome/test/chromedriver/navigation_tracker.cc

Index: chrome/test/chromedriver/navigation_tracker.cc
diff --git a/chrome/test/chromedriver/navigation_tracker.cc b/chrome/test/chromedriver/navigation_tracker.cc
index 4d9625041cc111182a9faf4b6df03b293bfed381..8c042f55291f3b93d410db465452ceaed8b850db 100644
--- a/chrome/test/chromedriver/navigation_tracker.cc
+++ b/chrome/test/chromedriver/navigation_tracker.cc
@@ -12,6 +12,13 @@ NavigationTracker::NavigationTracker() {}
 
 NavigationTracker::~NavigationTracker() {}
 
+Status NavigationTracker::Init(DevToolsClient* client) {
+  // Enable page domain notifications to allow tracking navigation state.
+  base::DictionaryValue params;
+  DCHECK(client);
+  return client->SendCommand("Page.enable", params);
+}
+
 bool NavigationTracker::IsPendingNavigation(const std::string& frame_id) {
   return frame_state_[frame_id].IsPendingNavigation();
 }