Fixing expiration of ScaledLinearHistogram to no longer segfault

Bug: 1088051
Change-Id: Ib400d10aa0c7e92d1bd0fa8a7071ed89a7306a3a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2293262
Commit-Queue: Joshua Berenhaus <joshber@microsoft.com>
Auto-Submit: Joshua Berenhaus <joshber@microsoft.com>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#787784}

base/metrics/histogram.cc

@@ -1084,12 +1084,19 @@ ScaledLinearHistogram::ScaledLinearHistogram(const std::string& name,
   CHECK_EQ(static_cast<Sample>(bucket_count), maximum - minimum + 2)
       << " ScaledLinearHistogram requires buckets of size 1";
 
+  // Normally, |histogram_| should have type LINEAR_HISTOGRAM or be
+  // inherited from it. However, if it's expired, it will be DUMMY_HISTOGRAM.
+  if (histogram_->GetHistogramType() == DUMMY_HISTOGRAM)
+    return;
+
   remainders_.resize(histogram_->bucket_count(), 0);
 }
 
 ScaledLinearHistogram::~ScaledLinearHistogram() = default;
 
 void ScaledLinearHistogram::AddScaledCount(Sample value, int count) {
+  if (histogram_->GetHistogramType() == DUMMY_HISTOGRAM)
+    return;
   if (count == 0)
     return;
   if (count < 0) {

base/metrics/histogram_unittest.cc

@@ -872,6 +872,13 @@ TEST_P(HistogramTest, ExpiredHistogramTest) {
   samples = linear_expired->SnapshotDelta();
   EXPECT_EQ(0, samples->TotalCount());
 
+  ScaledLinearHistogram scaled_linear_expired(kExpiredHistogramName, 1, 5, 6,
+                                              100, HistogramBase::kNoFlags);
+  scaled_linear_expired.AddScaledCount(0, 1);
+  scaled_linear_expired.AddScaledCount(1, 49);
+  samples = scaled_linear_expired.histogram()->SnapshotDelta();
+  EXPECT_EQ(0, samples->TotalCount());
+
   std::vector<int> custom_ranges;
   custom_ranges.push_back(1);
   custom_ranges.push_back(5);