SparseHistogram: Extract header ASCII drawing code

Extract header ASCII graphic emitting code (WriteAsciiHeader) out of
the histogram content drawing method (WriteAsciiImpl) to add more
flexibility in style setup.
Rename method [WriteAsciiImpl] to [WriteAsciiBody].
Move newline symbols to constants.

R=dcheng@chromium.org, sinhak@chromium.org

Bug: 1006447
Change-Id: If4af4c82efffaca10a0c34a9bb8abc98000235b7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2019204
Commit-Queue: Andrei Salavei <solovey@google.com>
Reviewed-by: Kush Sinha <sinhak@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735388}

base/metrics/sparse_histogram.cc

@@ -17,6 +17,11 @@
 #include "base/strings/stringprintf.h"
 #include "base/synchronization/lock.h"
 
+namespace {
+constexpr char kHtmlNewLine[] = "<br>";
+constexpr char kAsciiNewLine[] = "\n";
+}  // namespace
+
 namespace base {
 
 typedef HistogramBase::Count Count;
@@ -164,13 +169,23 @@ bool SparseHistogram::AddSamplesFromPickle(PickleIterator* iter) {
 }
 
 void SparseHistogram::WriteHTMLGraph(std::string* output) const {
+  // Get a local copy of the data so we are consistent.
+  std::unique_ptr<HistogramSamples> snapshot = SnapshotSamples();
+
   output->append("<PRE>");
-  WriteAsciiImpl(true, "<br>", output);
+  WriteAsciiHeader(*snapshot, output);
+  output->append(kHtmlNewLine);
+  WriteAsciiBody(*snapshot, true, kHtmlNewLine, output);
   output->append("</PRE>");
 }
 
 void SparseHistogram::WriteAscii(std::string* output) const {
-  WriteAsciiImpl(true, "\n", output);
+  // Get a local copy of the data so we are consistent.
+  std::unique_ptr<HistogramSamples> snapshot = SnapshotSamples();
+
+  WriteAsciiHeader(*snapshot, output);
+  output->append(kAsciiNewLine);
+  WriteAsciiBody(*snapshot, true, kAsciiNewLine, output);
 }
 
 void SparseHistogram::SerializeInfoImpl(Pickle* pickle) const {
@@ -227,24 +242,20 @@ void SparseHistogram::GetCountAndBucketData(Count* count,
   // TODO(kaiwang): Implement. (See HistogramBase::WriteJSON.)
 }
 
-void SparseHistogram::WriteAsciiImpl(bool graph_it,
+void SparseHistogram::WriteAsciiBody(const HistogramSamples& snapshot,
+                                     bool graph_it,
                                      const std::string& newline,
                                      std::string* output) const {
-  // Get a local copy of the data so we are consistent.
-  std::unique_ptr<HistogramSamples> snapshot = SnapshotSamples();
-  Count total_count = snapshot->TotalCount();
+  Count total_count = snapshot.TotalCount();
   double scaled_total_count = total_count / 100.0;
 
-  WriteAsciiHeader(total_count, output);
-  output->append(newline);
-
   // Determine how wide the largest bucket range is (how many digits to print),
   // so that we'll be able to right-align starts for the graphical bars.
   // Determine which bucket has the largest sample count so that we can
   // normalize the graphical bar-width relative to that sample count.
   Count largest_count = 0;
   Sample largest_sample = 0;
-  std::unique_ptr<SampleCountIterator> it = snapshot->Iterator();
+  std::unique_ptr<SampleCountIterator> it = snapshot.Iterator();
   while (!it->Done()) {
     Sample min;
     int64_t max;
@@ -259,7 +270,7 @@ void SparseHistogram::WriteAsciiImpl(bool graph_it,
   size_t print_width = GetSimpleAsciiBucketRange(largest_sample).size() + 1;
 
   // iterate over each item and display them
-  it = snapshot->Iterator();
+  it = snapshot.Iterator();
   while (!it->Done()) {
     Sample min;
     int64_t max;
@@ -280,10 +291,10 @@ void SparseHistogram::WriteAsciiImpl(bool graph_it,
   }
 }
 
-void SparseHistogram::WriteAsciiHeader(const Count total_count,
+void SparseHistogram::WriteAsciiHeader(const HistogramSamples& snapshot,
                                        std::string* output) const {
   StringAppendF(output, "Histogram: %s recorded %d samples", histogram_name(),
-                total_count);
+                snapshot.TotalCount());
   if (flags())
     StringAppendF(output, " (flags = 0x%x)", flags());
 }

base/metrics/sparse_histogram.h

@@ -80,12 +80,13 @@ class BASE_EXPORT SparseHistogram : public HistogramBase {
                              ListValue* buckets) const override;
 
   // Helpers for emitting Ascii graphic.  Each method appends data to output.
-  void WriteAsciiImpl(bool graph_it,
+  void WriteAsciiBody(const HistogramSamples& snapshot,
+                      bool graph_it,
                       const std::string& newline,
                       std::string* output) const;
 
   // Write a common header message describing this histogram.
-  void WriteAsciiHeader(const Count total_count,
+  void WriteAsciiHeader(const HistogramSamples& snapshot,
                         std::string* output) const;
 
   // For constuctor calling.