Remove std::string histogram name from HistogramBase object.

base/metrics/sparse_histogram.h

Index: base/metrics/sparse_histogram.h
diff --git a/base/metrics/sparse_histogram.h b/base/metrics/sparse_histogram.h
index 66e9825918d967f7298e6d82eb18992fdfae660f..851b6f629b91dd12cb091443de54c24f63d34b76 100644
--- a/base/metrics/sparse_histogram.h
+++ b/base/metrics/sparse_histogram.h
@@ -35,7 +35,7 @@ class BASE_EXPORT SparseHistogram : public HistogramBase {
   // live longer than the created sparse histogram.
   static std::unique_ptr<HistogramBase> PersistentCreate(
       PersistentHistogramAllocator* allocator,
-      const std::string& name,
+      const char* name,
       HistogramSamples::Metadata* meta,
       HistogramSamples::Metadata* logged_meta);
 
@@ -63,10 +63,10 @@ class BASE_EXPORT SparseHistogram : public HistogramBase {
 
  private:
   // Clients should always use FactoryGet to create SparseHistogram.
-  explicit SparseHistogram(const std::string& name);
+  explicit SparseHistogram(const char* name);
 
   SparseHistogram(PersistentHistogramAllocator* allocator,
-                  const std::string& name,
+                  const char* name,
                   HistogramSamples::Metadata* meta,
                   HistogramSamples::Metadata* logged_meta);