Telemetry: Add tests which would've caught the memory_benchmark breakage.

tools/telemetry/telemetry/page_benchmark_results_unittest.py

Index: tools/telemetry/telemetry/page_benchmark_results_unittest.py
diff --git a/tools/telemetry/telemetry/page_benchmark_results_unittest.py b/tools/telemetry/telemetry/page_benchmark_results_unittest.py
index fec3aafcbbe0cd7e6789a16241e216b6edb035a5..f2e5ab2f0b9596e6b36c237a644d6e2acc3ab10c 100644
--- a/tools/telemetry/telemetry/page_benchmark_results_unittest.py
+++ b/tools/telemetry/telemetry/page_benchmark_results_unittest.py
@@ -105,3 +105,32 @@ class PageBenchmarkResultsTest(unittest.TestCase):
     self.assertEquals(
       benchmark_results.results,
       expected)
+
+  def test_histogram(self):
+    page_set = _MakePageSet()
+
+    benchmark_results = SummarySavingPageBenchmarkResults()
+    benchmark_results.WillMeasurePage(page_set.pages[0])
+    benchmark_results.Add('a', '',
+                          '{"buckets": [{"low": 1, "high": 2, "count": 1}]}',
+                          data_type='histogram')
+    benchmark_results.DidMeasurePage()
+
+    benchmark_results.WillMeasurePage(page_set.pages[1])
+    benchmark_results.Add('a', '',
+                          '{"buckets": [{"low": 2, "high": 3, "count": 1}]}',
+                          data_type='histogram')
+    benchmark_results.DidMeasurePage()
+
+    benchmark_results.PrintSummary(None)
+
+    expected = [
+        '*HISTOGRAM a_by_url.http___www.foo.com_: ' +
+        'a_by_url.http___www.foo.com_= ' +
+        '{"buckets": [{"low": 1, "high": 2, "count": 1}]}\n' +
+        'Avg a_by_url.http___www.foo.com_: 1.500000',
+        '*HISTOGRAM a_by_url.http___www.bar.com_: ' +
+        'a_by_url.http___www.bar.com_= ' +
+        '{"buckets": [{"low": 2, "high": 3, "count": 1}]}\n' +
+        'Avg a_by_url.http___www.bar.com_: 2.500000']
+    self.assertEquals(benchmark_results.results, expected)