Support "shared" histograms between processes.

base/metrics/histogram_delta_serialization_unittest.cc

Index: base/metrics/histogram_delta_serialization_unittest.cc
diff --git a/base/metrics/histogram_delta_serialization_unittest.cc b/base/metrics/histogram_delta_serialization_unittest.cc
index b53520c5098787539d7d14691597cf125fde7be3..93f719826f3e7f207077ef65d1fbc7e84476aae5 100644
--- a/base/metrics/histogram_delta_serialization_unittest.cc
+++ b/base/metrics/histogram_delta_serialization_unittest.cc
@@ -18,7 +18,7 @@ TEST(HistogramDeltaSerializationTest, DeserializeHistogramAndAddSamples) {
   HistogramDeltaSerialization serializer("HistogramDeltaSerializationTest");
   std::vector<std::string> deltas;
   // Nothing was changed yet.
-  serializer.PrepareAndSerializeDeltas(&deltas);
+  serializer.PrepareAndSerializeDeltas(&deltas, true);
   EXPECT_TRUE(deltas.empty());
 
   HistogramBase* histogram = Histogram::FactoryGet(
@@ -28,7 +28,7 @@ TEST(HistogramDeltaSerializationTest, DeserializeHistogramAndAddSamples) {
   histogram->Add(100);
   histogram->Add(1000);
 
-  serializer.PrepareAndSerializeDeltas(&deltas);
+  serializer.PrepareAndSerializeDeltas(&deltas, true);
   EXPECT_FALSE(deltas.empty());
 
   HistogramDeltaSerialization::DeserializeAndAddSamples(deltas);