Prepare for applying opsz also when font-variation-settings not present

Add null check for font-variation-settings, rephrase reconfigured and
found axes.

TEST: virtual/text-antialias/mac-system-ui-trak.html
Bug: 1005969
Change-Id: If235b4518c801fe46bd5a7deb64d102310bc50f3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2022709
Commit-Queue: Dominik Röttsches <drott@chromium.org>
Commit-Queue: Ben Wagner <bungeman@chromium.org>
Reviewed-by: Ben Wagner <bungeman@chromium.org>
Auto-Submit: Dominik Röttsches <drott@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735404}

third_party/blink/renderer/platform/fonts/mac/font_platform_data_mac.mm

@@ -167,28 +167,28 @@ std::unique_ptr<FontPlatformData> FontPlatformDataFromNSFont(
 
   // Iterate over the font's axes and find a missing tag from variation
   // settings, special case opsz, track the number of axes reconfigured.
-  size_t reconfigured_axes = 0;
+  bool axes_reconfigured = false;
   for (auto& coordinate : coordinates_to_set) {
-    FontVariationAxis current_axis(AtomicString(), 0);
     // Set opsz to font size but allow having it overriden by
     // font-variation-settings in case it has 'opsz'.
     if (coordinate.axis == kOpszTag) {
       if (coordinate.value != SkFloatToScalar(size)) {
         coordinate.value = SkFloatToScalar(size);
-        reconfigured_axes++;
+        axes_reconfigured = true;
       }
     }
-    if (variation_settings->FindPair(FourByteTagToAtomicString(coordinate.axis),
-                                     &current_axis)) {
-      if (coordinate.value != current_axis.Value() &&
-          coordinate.axis != kOpszTag) {
-        coordinate.value = current_axis.Value();
-        reconfigured_axes++;
+    FontVariationAxis found_variation_setting(AtomicString(), 0);
+    if (variation_settings &&
+        variation_settings->FindPair(FourByteTagToAtomicString(coordinate.axis),
+                                     &found_variation_setting)) {
+      if (coordinate.value != found_variation_setting.Value()) {
+        coordinate.value = found_variation_setting.Value();
+        axes_reconfigured = true;
       }
     }
   }
 
-  if (!reconfigured_axes) {
+  if (!axes_reconfigured) {
     // No variable axes touched, return the previous typeface.
     return make_typeface_fontplatformdata();
   }

third_party/blink/renderer/platform/fonts/opentype/font_settings_test.cc

@@ -80,4 +80,11 @@ TEST(FontSettingsTest, FindTest) {
   }
 }
 
+TEST(FontSettingsTest, FindTestEmpty) {
+  scoped_refptr<FontVariationSettings> settings =
+      MakeSettings<FontVariationSettings, FontVariationAxis>({});
+  FontVariationAxis found_axis(AtomicString(), 0);
+  ASSERT_FALSE(settings->FindPair("a", &found_axis));
+}
+
 }  // namespace blink