Moved scoped_histogram_timer to the main histogram_macros.h.

base/metrics/histogram_macros.h

Index: base/metrics/histogram_macros.h
diff --git a/base/metrics/histogram_macros.h b/base/metrics/histogram_macros.h
index e9a871c358f71860f8314cd4510eb3bab6285132..87e0338dea369a43d671aab044c04eafd2062dcc 100644
--- a/base/metrics/histogram_macros.h
+++ b/base/metrics/histogram_macros.h
@@ -229,4 +229,25 @@
         base::CustomHistogram::FactoryGet(name, custom_ranges, \
             base::HistogramBase::kUmaTargetedHistogramFlag))
 
+// Scoped class which logs its time on this earth as a UMA statistic.  Must be
+// a #define macro since UMA macros prevent variables as names.  The nested
+// macro is necessary to expand __COUNTER__ to an actual value.
+#define SCOPED_UMA_HISTOGRAM_TIMER(name) \
+  SCOPED_UMA_HISTOGRAM_TIMER_EXPANDER(name, __COUNTER__)
+
+#define SCOPED_UMA_HISTOGRAM_TIMER_EXPANDER(name, key) \
+  SCOPED_UMA_HISTOGRAM_TIMER_UNIQUE(name, key)
+
+#define SCOPED_UMA_HISTOGRAM_TIMER_UNIQUE(name, key) \
+  class ScopedHistogramTimer##key { \
+   public: \
+    ScopedHistogramTimer##key() : constructed_(base::TimeTicks::Now()) {} \
+    ~ScopedHistogramTimer##key() { \
+      base::TimeDelta elapsed = base::TimeTicks::Now() - constructed_; \
+      UMA_HISTOGRAM_TIMES(name, elapsed); \
+    } \
+   private: \
+    base::TimeTicks constructed_; \
+  } scoped_histogram_timer_##key
+
 #endif  // BASE_METRICS_HISTOGRAM_MACROS_H_