[Chromecast] Update weighted mean to accept any numeric value

Change-Id: I288e3b7becaf926bef5fb61cb0bdd1c215cca31a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2108986Reviewed-by: Yuchen Liu <yucliu@chromium.org>
Commit-Queue: Kenneth MacKay <kmackay@chromium.org>
Cr-Commit-Position: refs/heads/master@{#751561}

chromecast/base/statistics/weighted_mean.cc

@@ -14,7 +14,7 @@ WeightedMean::WeightedMean()
       sum_weights_(0),
       sum_squared_weights_(0) {}
 
-void WeightedMean::AddSample(int64_t value, double weight) {
+void WeightedMean::AddDelta(double delta, double weight) {
   double old_sum_weights = sum_weights_;
   sum_weights_ += weight;
   // Use std::abs() to handle negative weights (ie, removing a sample).
@@ -23,7 +23,6 @@ void WeightedMean::AddSample(int64_t value, double weight) {
     weighted_mean_ = 0;
     variance_sum_ = 0;
   } else {
-    double delta = value - weighted_mean_;
     double mean_change = delta * weight / sum_weights_;
     weighted_mean_ += mean_change;
     variance_sum_ += old_sum_weights * delta * mean_change;

chromecast/base/statistics/weighted_mean.h

@@ -23,9 +23,14 @@ class WeightedMean {
 
   // Adds |value| to the mean if |weight| is positive. Removes |value| from
   // the mean if |weight| is negative. Has no effect if |weight| is 0.
-  void AddSample(int64_t value, double weight);
+  template <typename T>
+  void AddSample(T value, double weight) {
+    AddDelta(value - weighted_mean_, weight);
+  }
 
  private:
+  void AddDelta(double delta, double weight);
+
   double weighted_mean_;
   double variance_sum_;
   double sum_weights_;