Mark the AtomicString(const String&) constructor as explicit

Source/core/frame/FrameView.cpp

Index: Source/core/frame/FrameView.cpp
diff --git a/Source/core/frame/FrameView.cpp b/Source/core/frame/FrameView.cpp
index 8e541dbcf7876b8c1adc4bd5a113fcf1ad8646a8..87d288703323c67d095ffda4e99401540064f7ac 100644
--- a/Source/core/frame/FrameView.cpp
+++ b/Source/core/frame/FrameView.cpp
@@ -1282,7 +1282,7 @@ AtomicString FrameView::mediaType() const
     String overrideType;
     InspectorInstrumentation::applyEmulatedMedia(m_frame.get(), &overrideType);
     if (!overrideType.isNull())
-        return overrideType;
+        return AtomicString(overrideType);
     return m_mediaType;
 }