Add UMA histogram to track the various sources that request the feedback app

chrome/browser/supervised_user/supervised_user_interstitial.cc

 // Copyright 2014 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/supervised_user/supervised_user_interstitial.h"
 
 #include <stddef.h>
 
 #include "base/memory/weak_ptr.h"
 #include "base/metrics/histogram_macros.h"
@@ skipping 253 matching lines @@
     base::string16 reason =
         l10n_util::GetStringUTF16(supervised_user_error_page::GetBlockMessageID(
             reason_, true, second_custodian.empty()));
     std::string message = l10n_util::GetStringFUTF8(
         IDS_BLOCK_INTERSTITIAL_DEFAULT_FEEDBACK_TEXT, reason);
 #if defined(OS_ANDROID)
     DCHECK(profile_->IsChild());
     ReportChildAccountFeedback(web_contents_, message, url_);
 #else
     chrome::ShowFeedbackPage(chrome::FindBrowserWithWebContents(web_contents_),
-                             message, std::string());
+                             chrome::kFeedbackSourceSupervisedUserInterstitial,
+                             message, "" /* category_tag */);

[Lei Zhang, 2017/04/27 21:25:07]

Leave the std::string()s alone. Since ShowFeedbackPage() takes a std::string()
by const-ref, pass in a std::string to avoid the implicit construction.
Apparently that causes the compiler to generate a lot of code.

Ditto elsewhere.

[afakhry, 2017/04/27 21:39:54]

Done.

 #endif
     return;
   }
 
   NOTREACHED();
 }
 
 void SupervisedUserInterstitial::OnProceed() {
   DispatchContinueRequest(true);
 }
@@ skipping 62 matching lines @@
       SupervisedUserServiceFactory::GetForProfile(profile_);
   supervised_user_service->RemoveObserver(this);
 
   if (!callback_.is_null())
     callback_.Run(continue_request);
 
   // After this, the WebContents may be destroyed. Make sure we don't try to use
   // it again.
   web_contents_ = nullptr;
 }