Bug 837271 - part 1 - add means to control computation of extended statistics to histogram code; r=vladan

ipc/chromium/src/base/histogram.cc

@@ -559,7 +559,8 @@ const std::string Histogram::GetAsciiBucketRange(size_t i) const {
 // Update histogram data with new sample.
 void Histogram::Accumulate(Sample value, Count count, size_t index) {
   // Note locking not done in this version!!!
-  sample_.AccumulateWithExponentialStats(value, count, index);
+  sample_.AccumulateWithExponentialStats(value, count, index,
+					 flags_ & kExtendedStatisticsFlag);
 }
 
 void Histogram::SetBucketRange(size_t i, Sample value) {
@@ -743,12 +744,15 @@ void Histogram::SampleSet::AccumulateWithLinearStats(Sample value,
 
 void Histogram::SampleSet::AccumulateWithExponentialStats(Sample value,
                                                           Count count,
-                                                          size_t index) {
+                                                          size_t index,
+							  bool computeExtendedStatistics) {
   Accumulate(value, count, index);
-  DCHECK_GE(value, 0);
-  float value_log = logf(static_cast<float>(value) + 1.0f);
-  log_sum_ += count * value_log;
-  log_sum_squares_ += count * value_log * value_log;
+  if (computeExtendedStatistics) {
+    DCHECK_GE(value, 0);
+    float value_log = logf(static_cast<float>(value) + 1.0f);
+    log_sum_ += count * value_log;
+    log_sum_squares_ += count * value_log * value_log;
+  }
 }
 
 Count Histogram::SampleSet::TotalCount() const {

ipc/chromium/src/base/histogram.h

@@ -290,6 +290,7 @@ class Histogram {
   enum Flags {
     kNoFlags = 0,
     kUmaTargetedHistogramFlag = 0x1,  // Histogram should be UMA uploaded.
+    kExtendedStatisticsFlag = 0x2, // OK to gather extended statistics on histograms.
 
     // Indicate that the histogram was pickled to be sent across an IPC Channel.
     // If we observe this flag on a histogram being aggregated into after IPC,
@@ -336,7 +337,9 @@ class Histogram {
     // Accessor for histogram to make routine additions.
     void AccumulateWithLinearStats(Sample value, Count count, size_t index);
     // Alternate routine for exponential histograms.
-    void AccumulateWithExponentialStats(Sample value, Count count, size_t index);
+    // computeExpensiveStatistics should be true if we want to compute log sums.
+    void AccumulateWithExponentialStats(Sample value, Count count, size_t index,
+					bool computeExtendedStatistics);
 
     // Accessor methods.
     Count counts(size_t i) const { return counts_[i]; }