Fix Histogram shadowing warning on vs2015

d:\src\cr3\src\base\metrics\histogram.cc(498): warning C4457: declaration of 'count' hides function parameter
d:\src\cr3\src\base\metrics\histogram.cc(490): note: see declaration of 'count'

R=isherman@chromium.org
BUG=440500

Review URL: https://codereview.chromium.org/878223002

Cr-Commit-Position: refs/heads/master@{#313361}

base/metrics/histogram.cc

@@ -495,13 +495,13 @@ void Histogram::GetCountAndBucketData(Count* count,
   *sum = snapshot->sum();
   size_t index = 0;
   for (size_t i = 0; i < bucket_count(); ++i) {
-    Sample count = snapshot->GetCountAtIndex(i);
-    if (count > 0) {
+    Sample count_at_index = snapshot->GetCountAtIndex(i);
+    if (count_at_index > 0) {
       scoped_ptr<DictionaryValue> bucket_value(new DictionaryValue());
       bucket_value->SetInteger("low", ranges(i));
       if (i != bucket_count() - 1)
         bucket_value->SetInteger("high", ranges(i + 1));
-      bucket_value->SetInteger("count", count);
+      bucket_value->SetInteger("count", count_at_index);
       buckets->Set(index, bucket_value.release());
       ++index;
     }