Add Sparse Histogram Support to metricsPrivate

chrome/test/data/extensions/api_test/metrics/test.js

Index: chrome/test/data/extensions/api_test/metrics/test.js
diff --git a/chrome/test/data/extensions/api_test/metrics/test.js b/chrome/test/data/extensions/api_test/metrics/test.js
index 619a14176027912e9a3716845a25e43861258545..650e586106f393052651bd82f62b9dc2090e11ee 100644
--- a/chrome/test/data/extensions/api_test/metrics/test.js
+++ b/chrome/test/data/extensions/api_test/metrics/test.js
@@ -43,6 +43,14 @@ chrome.test.runTests([
     chrome.test.succeed();
   },
 
+  function recordSparseValue() {
+    chrome.metricsPrivate.recordSparseValue('test.sparse.1', 42);
+    chrome.metricsPrivate.recordSparseValue('test.sparse.2', 24);
+    chrome.metricsPrivate.recordSparseValue('test.sparse.2', 24);

[Ilya Sherman, 2014/03/26 22:44:14]

What I really meant was that it would be nice to verify that for a single sparse
histogram, it's possible to emit to multiple buckets.

[robliao, 2014/03/26 23:37:54]

Done.

+
+    chrome.test.succeed();
+  },
+
   function recordTimes() {
     chrome.metricsPrivate.recordTime('test.time', 42);
     chrome.metricsPrivate.recordMediumTime('test.medium.time', 42 * 1000);