UKM that threads together multiple form interaction events.

components/ukm/test_ukm_service.cc

Index: components/ukm/test_ukm_service.cc
diff --git a/components/ukm/test_ukm_service.cc b/components/ukm/test_ukm_service.cc
index e3fcef8671e1102941eae8d3b541227b3e71d5ad..824fa25a7fe2df7a21233a271bcd40eb21c14acb 100644
--- a/components/ukm/test_ukm_service.cc
+++ b/components/ukm/test_ukm_service.cc
@@ -4,6 +4,9 @@
 
 #include "components/ukm/test_ukm_service.h"
 
+#include "base/logging.h"
+#include "base/metrics/metrics_hashes.h"
+#include "components/ukm/ukm_entry.h"
 #include "components/ukm/ukm_source.h"
 
 namespace ukm {
@@ -33,15 +36,38 @@ TestUkmService::GetSources() const {
 }
 
 const UkmSource* TestUkmService::GetSourceForUrl(const char* url) const {
+  const UkmSource* source = nullptr;
   for (const auto& kv : sources_for_testing()) {
-    if (kv.second->url() == url)
-      return kv.second.get();
+    if (kv.second->url() == url) {
+      DCHECK_EQ(nullptr, source);
+      source = kv.second.get();
+    }
   }
-  return nullptr;
+  return source;
+}
+
+const UkmSource* TestUkmService::GetSourceForSourceId(int32_t source_id) const {
+  const UkmSource* source = nullptr;
+  for (const auto& kv : sources_for_testing()) {
+    if (kv.second->id() == source_id) {
+      DCHECK_EQ(nullptr, source);
+      source = kv.second.get();
+    }
+  }
+  return source;
 }
 
 const UkmEntry* TestUkmService::GetEntry(size_t entry_num) const {
   return entries_for_testing()[entry_num].get();
 }
 
+const UkmEntry* TestUkmService::GetEntryForEntryName(
+    const char* entry_name) const {
+  for (const auto& it : entries_for_testing()) {
+    if (it->event_hash() == base::HashMetricName(entry_name))
+      return it.get();
+  }
+  return nullptr;
+}
+
 }  // namespace ukm