[Extensions] Fix crash in chrome://extensions metrics

chrome/browser/ui/webui/extensions/extensions_ui.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/webui/extensions/extensions_ui.h"
 
 #include <memory>
 
 #include "base/metrics/histogram_macros.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 38 matching lines @@
   void DidStartProvisionalLoadForFrame(
       content::RenderFrameHost* render_frame_host,
       const GURL& validated_url,
       bool is_error_page,
       bool is_iframe_srcdoc) override {
     timer_.reset(new base::ElapsedTimer());
   }
 
   void DocumentLoadedInFrame(
       content::RenderFrameHost* render_frame_host) override {
-    if (render_frame_host != web_contents()->GetMainFrame())
+    if (render_frame_host != web_contents()->GetMainFrame() ||
+        !timer_) {  // See comment in DocumentOnLoadCompletedInMainFrame()
       return;
+    }
     if (is_md_) {
       UMA_HISTOGRAM_TIMES("Extensions.WebUi.DocumentLoadedInMainFrameTime.MD",
                           timer_->Elapsed());
     } else {
       UMA_HISTOGRAM_TIMES("Extensions.WebUi.DocumentLoadedInMainFrameTime.Uber",
                           timer_->Elapsed());
     }
   }
 
   void DocumentOnLoadCompletedInMainFrame() override {
+    // Sometimes*, DidStartProvisionalLoadForFrame() isn't called before this
+    // or DocumentLoadedInFrame(). Don't log anything in those cases.
+    // *This appears to be for in-page navigations like hash changes.
+    // TODO(devlin): The usefulness of these metrics remains to be seen.
+    if (!timer_)
+      return;
     if (is_md_) {
       UMA_HISTOGRAM_TIMES("Extensions.WebUi.LoadCompletedInMainFrame.MD",
                           timer_->Elapsed());
     } else {
       UMA_HISTOGRAM_TIMES("Extensions.WebUi.LoadCompletedInMainFrame.Uber",
                           timer_->Elapsed());
     }
+    timer_.reset();
   }
 
   void WebContentsDestroyed() override { delete this; }
 
  private:
   // Whether this is the MD version of the chrome://extensions page.
   bool is_md_;
 
   std::unique_ptr<base::ElapsedTimer> timer_;
 
@@ skipping 232 matching lines @@
 ExtensionsUI::~ExtensionsUI() {}
 
 // static
 base::RefCountedMemory* ExtensionsUI::GetFaviconResourceBytes(
     ui::ScaleFactor scale_factor) {
   ui::ResourceBundle& rb = ui::ResourceBundle::GetSharedInstance();
   return rb.LoadDataResourceBytesForScale(IDR_EXTENSIONS_FAVICON, scale_factor);
 }
 
 }  // namespace extensions