Fix overflow when logging MaxInt32 to a sparse histogram.

chrome/browser/ui/webui/task_scheduler_internals/task_scheduler_internals_ui.cc

 // Copyright 2016 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/task_scheduler_internals/task_scheduler_internals_ui.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/memory/ptr_util.h"
@@ skipping 12 matching lines @@
 std::unique_ptr<base::Value> SnapshotHistogramToValue(
     const base::HistogramBase* histogram) {
   std::unique_ptr<base::ListValue> values =
       base::MakeUnique<base::ListValue>();
 
   std::unique_ptr<base::HistogramSamples> samples =
       histogram->SnapshotSamples();
   std::unique_ptr<base::SampleCountIterator> iterator = samples->Iterator();
   while (!iterator->Done()) {
     base::HistogramBase::Sample min;
-    base::HistogramBase::Sample max;
+    int64_t max;
     base::HistogramBase::Count count;
     iterator->Get(&min, &max, &count);
 
     std::unique_ptr<base::DictionaryValue> bucket =
         base::MakeUnique<base::DictionaryValue>();
     bucket->SetInteger("min", min);
-    bucket->SetInteger("max", max);
+    // Note: DictionaryValue does not support 64-bit integer values. The static
+    // cast below is OK in this case because none of the histograms passed to
+    // this function should be logging MaxInt32 as a sparse histogram bucket,
+    // which is the only case max will exceed 32-bit range.
+    bucket->SetInteger("max", static_cast<int>(max));

[Ilya Sherman, 2017/05/02 21:37:49]

nit: Could this be a checked_cast?

[Alexei Svitkine (slow), 2017/05/03 15:21:53]

Done.

     bucket->SetInteger("count", count);
 
     values->Append(std::move(bucket));
     iterator->Next();
   }
   return std::move(values);
 }
 
 class TaskSchedulerDataHandler : public content::WebUIMessageHandler {
  public:
@@ skipping 52 matching lines @@
       "index.css", IDR_TASK_SCHEDULER_INTERNALS_RESOURCES_INDEX_CSS);
   html_source->AddResourcePath(
       "index.js", IDR_TASK_SCHEDULER_INTERNALS_RESOURCES_INDEX_JS);
   html_source->SetDefaultResource(
       IDR_TASK_SCHEDULER_INTERNALS_RESOURCES_INDEX_HTML);
 
   content::WebUIDataSource::Add(Profile::FromWebUI(web_ui), html_source);
 }
 
 TaskSchedulerInternalsUI::~TaskSchedulerInternalsUI() = default;