Fix of unused variable warnings related to DHISTOGRAM* in release builds.

    
Make DHISTOGRAM* keep a mention of passed variables.
Add Histogram::DebugNow() for use in DHISTOGRAM* as a start_time.


BUG=87490
TEST=None


Review URL: http://codereview.chromium.org/8225001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@105722 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 50 insertions, 8 deletions

diff --git a/base/metrics/histogram.cc b/base/metrics/histogram.cc
index dbd7278..8b11ee8 100644
--- a/base/metrics/histogram.cc
+++ b/base/metrics/histogram.cc
@@ -114,6 +114,14 @@ Histogram* Histogram::FactoryTimeGet(const std::string& name,
                     bucket_count, flags);
 }
 
+TimeTicks Histogram::DebugNow() {
+#ifndef NDEBUG
+  return TimeTicks::Now();
+#else
+  return TimeTicks();
+#endif
+}
+
 void Histogram::Add(int value) {
   if (value > kSampleType_MAX - 1)
     value = kSampleType_MAX - 1;
diff --git a/base/metrics/histogram.h b/base/metrics/histogram.h
index 401ece7..e8f6364 100644
--- a/base/metrics/histogram.h
+++ b/base/metrics/histogram.h
@@ -202,19 +202,50 @@ class Lock;
     HISTOGRAM_CUSTOM_ENUMERATION(name, sample, custom_ranges)
 
 #else  // NDEBUG
+// Keep a mention of passed variables to avoid unused variable warnings in
+// release build if these variables are only used in macros.
+#define DISCARD_2_ARGUMENTS(a, b) \
+  while (0) { \
+    static_cast<void>(a); \
+    static_cast<void>(b); \
+ }
+#define DISCARD_3_ARGUMENTS(a, b, c) \
+  while (0) { \
+    static_cast<void>(a); \
+    static_cast<void>(b); \
+    static_cast<void>(c); \
+ }
+#define DISCARD_5_ARGUMENTS(a, b, c, d ,e) \
+  while (0) { \
+    static_cast<void>(a); \
+    static_cast<void>(b); \
+    static_cast<void>(c); \
+    static_cast<void>(d); \
+    static_cast<void>(e); \
+ }
+#define DHISTOGRAM_TIMES(name, sample) \
+    DISCARD_2_ARGUMENTS(name, sample)
+
+#define DHISTOGRAM_COUNTS(name, sample) \
+    DISCARD_2_ARGUMENTS(name, sample)
+
+#define DHISTOGRAM_PERCENTAGE(name, under_one_hundred) \
+    DISCARD_2_ARGUMENTS(name, under_one_hundred)
 
-#define DHISTOGRAM_TIMES(name, sample) do {} while (0)
-#define DHISTOGRAM_COUNTS(name, sample) do {} while (0)
-#define DHISTOGRAM_PERCENTAGE(name, under_one_hundred) do {} while (0)
 #define DHISTOGRAM_CUSTOM_TIMES(name, sample, min, max, bucket_count) \
-    do {} while (0)
+    DISCARD_5_ARGUMENTS(name, sample, min, max, bucket_count)
+
 #define DHISTOGRAM_CLIPPED_TIMES(name, sample, min, max, bucket_count) \
-    do {} while (0)
+    DISCARD_5_ARGUMENTS(name, sample, min, max, bucket_count)
+
 #define DHISTOGRAM_CUSTOM_COUNTS(name, sample, min, max, bucket_count) \
-    do {} while (0)
-#define DHISTOGRAM_ENUMERATION(name, sample, boundary_value) do {} while (0)
+    DISCARD_5_ARGUMENTS(name, sample, min, max, bucket_count)
+
+#define DHISTOGRAM_ENUMERATION(name, sample, boundary_value) \
+    DISCARD_3_ARGUMENTS(name, sample, boundary_value)
+
 #define DHISTOGRAM_CUSTOM_ENUMERATION(name, sample, custom_ranges) \
-    do {} while (0)
+    DISCARD_3_ARGUMENTS(name, sample, custom_ranges)
 
 #endif  // NDEBUG
 
@@ -409,6 +440,9 @@ class BASE_EXPORT Histogram {
                                    base::TimeDelta maximum,
                                    size_t bucket_count,
                                    Flags flags);
+  // Time call for use with DHISTOGRAM*.
+  // Returns TimeTicks::Now() in debug and TimeTicks() in release build.
+  static TimeTicks DebugNow();
 
   void Add(int value);