[Structured metrics] Add unit test to check IDs shared within project

When two event definitions are grouped under a project, their recorded
events should share an user event ID. This adds a test to make sure
that's the case.

Bug: 1016655
Change-Id: I32476ece7dd80c7366230a456d5e9d8210355115
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2119457Reviewed-by: Thanh Nguyen <thanhdng@chromium.org>
Commit-Queue: Tony Yeoman <tby@chromium.org>
Cr-Commit-Position: refs/heads/master@{#754770}

components/metrics/structured/structured_metrics_provider_unittest.cc

@@ -58,6 +58,8 @@ constexpr char kKeyData[] = R"({
 constexpr uint64_t kEventOneHash = UINT64_C(15619026293081468407);
 // The name hash of "TestEventTwo".
 constexpr uint64_t kEventTwoHash = UINT64_C(15791833939776536363);
+// The name hash of "TestEventThree".
+constexpr uint64_t kEventThreeHash = UINT64_C(16464330721839207086);
 
 // The name hash of "TestMetricOne".
 constexpr uint64_t kMetricOneHash = UINT64_C(637929385654885975);
@@ -287,6 +289,36 @@ TEST_F(StructuredMetricsProviderTest, EventsReportedCorrectly) {
   histogram_tester_.ExpectTotalCount("UMA.StructuredMetrics.PrefReadError", 0);
 }
 
+TEST_F(StructuredMetricsProviderTest, EventsWithinProjectReportedWithSameID) {
+  WriteTestingKeys();
+  Init();
+
+  events::TestEventOne().Record();
+  events::TestEventTwo().Record();
+  events::TestEventThree().Record();
+
+  const auto uma = GetProvidedEvents();
+  ASSERT_EQ(uma.structured_event_size(), 3);
+
+  const auto& event_one = uma.structured_event(0);
+  const auto& event_two = uma.structured_event(1);
+  const auto& event_three = uma.structured_event(2);
+
+  // Check events are in the right order.
+  EXPECT_EQ(event_one.event_name_hash(), kEventOneHash);
+  EXPECT_EQ(event_two.event_name_hash(), kEventTwoHash);
+  EXPECT_EQ(event_three.event_name_hash(), kEventThreeHash);
+
+  // Events two and three share a project, so should have the same ID. Event
+  // one should have its own ID.
+  EXPECT_EQ(HashToHex(event_one.profile_event_id()), kKeyOneId);
+  EXPECT_EQ(HashToHex(event_two.profile_event_id()), kKeyTwoId);
+  EXPECT_EQ(HashToHex(event_three.profile_event_id()), kKeyTwoId);
+
+  histogram_tester_.ExpectTotalCount("UMA.StructuredMetrics.InternalError", 0);
+  histogram_tester_.ExpectTotalCount("UMA.StructuredMetrics.PrefReadError", 0);
+}
+
 // Test that a call to ProvideCurrentSessionData clears the provided events from
 // the cache, and a subsequent call does not return those events again.
 TEST_F(StructuredMetricsProviderTest, EventsClearedAfterReport) {