[SH] Handle Empty Referrer Case

The Search Engine check DCHECK's on empty URL. Empty Referrers exist,
so it's better to handle that case than DCHECK on it.

Bug: 1131107
Change-Id: Ic238ff86ccc6cee912baea37d8f549b99b685f50
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2480963Reviewed-by: sebsg <sebsg@chromium.org>
Commit-Queue: Sebastien Lalancette <seblalancette@chromium.org>
Cr-Commit-Position: refs/heads/master@{#818048}

components/shared_highlighting/core/common/shared_highlighting_metrics.cc

@@ -13,7 +13,8 @@ namespace shared_highlighting {
 namespace {
 
 TextFragmentLinkOpenSource GetLinkSource(const GURL& referrer) {
-  bool from_search_engine = SearchEngineUtils::GetEngineType(referrer) > 0;
+  bool from_search_engine =
+      referrer.is_valid() && SearchEngineUtils::GetEngineType(referrer) > 0;
   return from_search_engine ? TextFragmentLinkOpenSource::kSearchEngine
                             : TextFragmentLinkOpenSource::kUnknown;
 }

components/shared_highlighting/core/common/shared_highlighting_metrics_unittest.cc

@@ -26,15 +26,23 @@ TEST(SharedHighlightingMetricsTest, LogTextFragmentAmbiguousMatch) {
 TEST(SharedHighlightingMetricsTest, LogTextFragmentLinkOpenSource) {
   base::HistogramTester histogram_tester;
 
-  GURL search_engine_url = GURL("https://google.com");
-  GURL non_search_engine_url = GURL("https://example.com");
-
+  GURL search_engine_url("https://google.com");
   LogTextFragmentLinkOpenSource(search_engine_url);
-  histogram_tester.ExpectBucketCount("TextFragmentAnchor.LinkOpenSource", 1, 1);
+  histogram_tester.ExpectBucketCount("TextFragmentAnchor.LinkOpenSource",
+                                     TextFragmentLinkOpenSource::kSearchEngine,
+                                     1);
 
+  GURL non_search_engine_url("https://example.com");
   LogTextFragmentLinkOpenSource(non_search_engine_url);
-  histogram_tester.ExpectBucketCount("TextFragmentAnchor.LinkOpenSource", 0, 1);
+  histogram_tester.ExpectBucketCount("TextFragmentAnchor.LinkOpenSource",
+                                     TextFragmentLinkOpenSource::kUnknown, 1);
   histogram_tester.ExpectTotalCount("TextFragmentAnchor.LinkOpenSource", 2);
+
+  GURL empty_gurl("");
+  LogTextFragmentLinkOpenSource(empty_gurl);
+  histogram_tester.ExpectBucketCount("TextFragmentAnchor.LinkOpenSource",
+                                     TextFragmentLinkOpenSource::kUnknown, 2);
+  histogram_tester.ExpectTotalCount("TextFragmentAnchor.LinkOpenSource", 3);
 }
 
 TEST(SharedHighlightingMetricsTest, LogTextFragmentMatchRate) {