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

chrome/test/chromedriver/frame_tracker.cc

Index: chrome/test/chromedriver/frame_tracker.cc
diff --git a/chrome/test/chromedriver/frame_tracker.cc b/chrome/test/chromedriver/frame_tracker.cc
index e3354be6eb1e016dc078e98dfd9fba0d40f20061..39b85e6dd12f2786313fc4764964d15e093acaff 100644
--- a/chrome/test/chromedriver/frame_tracker.cc
+++ b/chrome/test/chromedriver/frame_tracker.cc
@@ -9,12 +9,20 @@
 #include "base/json/json_writer.h"
 #include "base/logging.h"
 #include "base/values.h"
+#include "chrome/test/chromedriver/devtools_client.h"
 #include "chrome/test/chromedriver/status.h"
 
 FrameTracker::FrameTracker() {}
 
 FrameTracker::~FrameTracker() {}
 
+Status FrameTracker::Init(DevToolsClient* client) {
+  // Enable runtime events to allow tracking execution context creation.
+  base::DictionaryValue params;
+  DCHECK(client);
+  return client->SendCommand("Runtime.enable", params);
+}
+
 Status FrameTracker::GetFrameForContextId(
     int context_id, std::string* frame_id) {
   if (context_to_frame_map_.count(context_id) == 0)