Fix various -Werror build failures

https://bugs.webkit.org/show_bug.cgi?id=256466

Unreviewed build fixes.

Fix unused variable warnings, plus placate Clang's overaggressive
-Wmissing-field-initializers in MiniBrowser.

* Source/WebCore/platform/mediastream/gstreamer/GStreamerMediaStreamSource.cpp:
* Tools/MiniBrowser/gtk/main.c:
(addSettingsGroupToContext):
* Tools/TestWebKitAPI/Tests/WebCore/FloatSizeTests.cpp:
(TestWebKitAPI::TEST):

Canonical link: https://commits.webkit.org/263801@main

Source/WebCore/platform/mediastream/gstreamer/GStreamerMediaStreamSource.cpp

@@ -124,8 +124,13 @@ class InternalSource final : public MediaStreamTrackPrivate::Observer,
         : m_parent(parent)
         , m_track(track)
         , m_padName(padName)
+#if USE(GSTREAMER_WEBRTC)
         , m_consumerIsVideoPlayer(consumerIsVideoPlayer)
+#endif
     {
+#if !USE(GSTREAMER_WEBRTC)
+        UNUSED_PARAM(consumerIsVideoPlayer);
+#endif
         static uint64_t audioCounter = 0;
         static uint64_t videoCounter = 0;
         String elementName;
@@ -536,7 +541,9 @@ class InternalSource final : public MediaStreamTrackPrivate::Observer,
     Lock m_eosLock;
     bool m_eosPending WTF_GUARDED_BY_LOCK(m_eosLock) { false };
     std::optional<int> m_webrtcSourceClientId;
+#if USE(GSTREAMER_WEBRTC)
     bool m_consumerIsVideoPlayer { false };
+#endif
 };
 
 struct _WebKitMediaStreamSrcPrivate {

Tools/MiniBrowser/gtk/main.c

@@ -384,8 +384,9 @@ static gboolean addSettingsGroupToContext(GOptionContext *context, WebKitSetting
             .arg_data = parseFeaturesOptionCallback,
             .arg_description = "FEATURE-LIST",
         },
-        { NULL }
+        { }
     };
+    memset(&featureEntries[1], 0, sizeof(GOptionEntry));
     g_option_group_add_entries(webSettingsGroup, featureEntries);
 
     /* Option context takes ownership of the group. */

Tools/TestWebKitAPI/Tests/WebCore/FloatSizeTests.cpp

@@ -190,9 +190,9 @@ TEST(FloatSize, TransposedSize)
 
 TEST(FloatSize, Casting)
 {
+#if USE(CG)
     WebCore::FloatSize test(1024.0f, 768.0f);
 
-#if USE(CG)
     CGSize cgSize = test;
 
     EXPECT_FLOAT_EQ(1024.0f, cgSize.width);