FontMatchingMetrics::InsertFontHashIntoMap should take a ref to the map

Currently, it creates a copy of the map, which means no metrics should be recorded.

Change-Id: I8d00d464e448fa364cfd47dd8657b3c4f650fff1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2590384
Auto-Submit: Alex Turner <alexmt@chromium.org>
Reviewed-by: Paul Jensen <pauljensen@chromium.org>
Reviewed-by: Dominik Röttsches <drott@chromium.org>
Commit-Queue: Dominik Röttsches <drott@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837118}

third_party/blink/renderer/platform/fonts/font_matching_metrics.cc

@@ -114,7 +114,7 @@ void FontMatchingMetrics::ReportLocalFontExistenceByUniqueNameOnly(
 
 void FontMatchingMetrics::InsertFontHashIntoMap(IdentifiableTokenKey input_key,
                                                 SimpleFontData* font_data,
-                                                TokenToTokenHashMap hash_map) {
+                                                TokenToTokenHashMap& hash_map) {
   DCHECK(IdentifiabilityStudySettings::Get()->IsActive());
   if (hash_map.Contains(input_key))
     return;

third_party/blink/renderer/platform/fonts/font_matching_metrics.h

@@ -198,7 +198,7 @@ class PLATFORM_EXPORT FontMatchingMetrics {
   // name in |font_load_postscript_name_|.
   void InsertFontHashIntoMap(IdentifiableTokenKey input_key,
                              SimpleFontData* font_data,
-                             TokenToTokenHashMap hash_map);
+                             TokenToTokenHashMap& hash_map);
 
   // Reports a local font's existence was looked up by a name, but its actual
   // font data may or may not have been loaded. This only includes lookups where