Add a force pipelining option to load flags.

chrome/browser/net/http_pipelining_compatibility_client_unittest.cc

Index: chrome/browser/net/http_pipelining_compatibility_client_unittest.cc
diff --git a/chrome/browser/net/http_pipelining_compatibility_client_unittest.cc b/chrome/browser/net/http_pipelining_compatibility_client_unittest.cc
index 39ebfcd3c5e68fe9a445269122a3c69c2ac6bbe2..eb9dd0f1313a95bc315e5a3ee35772d2d954594b 100644
--- a/chrome/browser/net/http_pipelining_compatibility_client_unittest.cc
+++ b/chrome/browser/net/http_pipelining_compatibility_client_unittest.cc
@@ -126,13 +126,32 @@ class HttpPipeliningCompatibilityClientTest : public testing::Test {
  private:
   base::Histogram::SampleSet GetHistogram(const char* name) {
     base::Histogram::SampleSet sample;
-    base::Histogram* histogram;
+    base::Histogram* current_histogram = NULL;
+    base::Histogram* cached_histogram = NULL;
+    base::StatisticsRecorder::FindHistogram(name, &current_histogram);
     if (ContainsKey(histograms_, name)) {
-      histogram = histograms_[name];
-      histogram->SnapshotSample(&sample);
-    } else if (base::StatisticsRecorder::FindHistogram(name, &histogram)) {
-      histograms_[name] = histogram;
-      histogram->SnapshotSample(&sample);
+      cached_histogram = histograms_[name];
+    }
+
+    // This is to work around the CACHE_HISTOGRAM_* macros caching the last used
+    // histogram by name. So, even though we throw out the StatisticsRecorder
+    // between tests, the CACHE_HISTOGRAM_* might still write into the old
+    // Histogram if it has the same name as the last run. We keep a cache of the
+    // last used Histogram and then update the cache if it's different than the
+    // current Histogram.

[mmenke, 2012/02/23 18:54:58]

Why was this working before, but is now causing problems?

[James Simonsen, 2012/02/23 23:49:46]

The old version was broken, but just happened to work. It assumed that once a
histogram was cached, that histogram should always be used. That's incorrect,
the UMA macro will update its cache if sees a different name. So we need to
update our cache in that situation too.

This is tickled now because the evictions finish out of order when we force
pipelining. We receive the evictions before the first request succeeds.

+    if (cached_histogram && current_histogram) {
+      cached_histogram->SnapshotSample(&sample);
+      if (cached_histogram != current_histogram) {
+        base::Histogram::SampleSet current_sample;
+        current_histogram->SnapshotSample(&current_sample);
+        sample.Add(current_sample);
+        histograms_[name] = current_histogram;
+      }
+    } else if (current_histogram) {
+      current_histogram->SnapshotSample(&sample);
+      histograms_[name] = current_histogram;
+    } else if (cached_histogram) {
+      cached_histogram->SnapshotSample(&sample);
     }
     return sample;
   }
@@ -415,7 +434,7 @@ TEST_F(HttpPipeliningCompatibilityClientTest, MultipleRequests) {
   base::Histogram::SampleSet network_sample2 =
       GetHistogramValue(1, FIELD_NETWORK_ERROR);
   EXPECT_EQ(1, network_sample2.TotalCount());
-  EXPECT_EQ(1, network_sample2.counts(-net::ERR_EMPTY_RESPONSE));
+  EXPECT_EQ(1, network_sample2.counts(-net::ERR_PIPELINE_EVICTION));
 
   base::Histogram::SampleSet response_sample2 =
       GetHistogramValue(1, FIELD_RESPONSE_CODE);
@@ -425,16 +444,16 @@ TEST_F(HttpPipeliningCompatibilityClientTest, MultipleRequests) {
       GetHistogramValue(2, FIELD_STATUS);
   EXPECT_EQ(1, status_sample3.TotalCount());
   EXPECT_EQ(1, status_sample3.counts(
-      HttpPipeliningCompatibilityClient::BAD_RESPONSE_CODE));
+      HttpPipeliningCompatibilityClient::NETWORK_ERROR));
 
   base::Histogram::SampleSet network_sample3 =
       GetHistogramValue(2, FIELD_NETWORK_ERROR);
-  EXPECT_EQ(0, network_sample3.TotalCount());
+  EXPECT_EQ(1, network_sample3.TotalCount());
+  EXPECT_EQ(1, network_sample3.counts(-net::ERR_PIPELINE_EVICTION));
 
   base::Histogram::SampleSet response_sample3 =
       GetHistogramValue(2, FIELD_RESPONSE_CODE);
-  EXPECT_EQ(1, response_sample3.TotalCount());
-  EXPECT_EQ(1, response_sample3.counts(401));
+  EXPECT_EQ(0, response_sample3.TotalCount());
 }
 
 }  // anonymous namespace