Add linearly spaced counting histograms

webrtc/system_wrappers/include/metrics.h

Index: webrtc/system_wrappers/include/metrics.h
diff --git a/webrtc/system_wrappers/include/metrics.h b/webrtc/system_wrappers/include/metrics.h
index 9b14736ec2eee4e4013e11fc8cf29def012a585d..25a51807dec0d6968950bb2e3ce13c8a5283ea33 100644
--- a/webrtc/system_wrappers/include/metrics.h
+++ b/webrtc/system_wrappers/include/metrics.h
@@ -85,6 +85,11 @@
   RTC_HISTOGRAM_COMMON_BLOCK(name, sample, \
       webrtc::metrics::HistogramFactoryGetCounts(name, min, max, bucket_count))
 
+#define RTC_HISTOGRAM_COUNTS_LINEAR(name, sample, min, max, bucket_count)      \
+  RTC_HISTOGRAM_COMMON_BLOCK(name, sample,                                     \
+                             webrtc::metrics::HistogramFactoryGetCountsLinear( \
+                                 name, min, max, bucket_count))
+
 // Deprecated.
 // TODO(asapersson): Remove.
 #define RTC_HISTOGRAM_COUNTS_SPARSE_100(name, sample) \
@@ -213,6 +218,12 @@ class Histogram;
 Histogram* HistogramFactoryGetCounts(
     const std::string& name, int min, int max, int bucket_count);
 
+// Get histogram for counters with linear bucket spacing.
+Histogram* HistogramFactoryGetCountsLinear(const std::string& name,
+                                           int min,
+                                           int max,
+                                           int bucket_count);
+
 // Get histogram for enumerators.
 // |boundary| should be above the max enumerator sample.
 Histogram* HistogramFactoryGetEnumeration(