[page_load_metrics] Add support for chrome:// urls and add extensions observer

chrome/renderer/page_load_metrics/renderer_page_track_decider.cc

Index: chrome/renderer/page_load_metrics/renderer_page_track_decider.cc
diff --git a/chrome/renderer/page_load_metrics/renderer_page_track_decider.cc b/chrome/renderer/page_load_metrics/renderer_page_track_decider.cc
index 861b13c351a121c6a60d991b23e97ff5e9e1a194..fa43321d13d39148114dcb18e6ef594bc7d10c3d 100644
--- a/chrome/renderer/page_load_metrics/renderer_page_track_decider.cc
+++ b/chrome/renderer/page_load_metrics/renderer_page_track_decider.cc
@@ -11,6 +11,7 @@
 #include "third_party/WebKit/public/web/WebDataSource.h"
 #include "third_party/WebKit/public/web/WebDocument.h"
 #include "url/gurl.h"
+#include "url/url_constants.h"
 
 namespace page_load_metrics {
 
@@ -26,14 +27,14 @@ bool RendererPageTrackDecider::HasCommitted() {
   return true;
 }
 
-bool RendererPageTrackDecider::IsHttpOrHttpsUrl() {
-  return static_cast<GURL>(document_->url()).SchemeIsHTTPOrHTTPS();
-}
-
 bool RendererPageTrackDecider::IsNewTabPageUrl() {
   return SearchBouncer::GetInstance()->IsNewTabPage(document_->url());
 }
 
+bool RendererPageTrackDecider::IsAboutBlankUrl() {
+  return document_->url().string() == url::kAboutBlankURL;
+}
+
 bool RendererPageTrackDecider::IsChromeErrorPage() {
   return data_source_->hasUnreachableURL();
 }