Merge the Sky Engine changes from the SkyDart branch

sky/engine/wtf/text/AtomicString.h

Index: sky/engine/wtf/text/AtomicString.h
diff --git a/sky/engine/wtf/text/AtomicString.h b/sky/engine/wtf/text/AtomicString.h
index 4da69513f94762ab1b45805a2422ea7ec1618f15..b858924fb6d1057764f911b1d2a7151008315e24 100644
--- a/sky/engine/wtf/text/AtomicString.h
+++ b/sky/engine/wtf/text/AtomicString.h
@@ -51,7 +51,7 @@ public:
     // Constructing an AtomicString from a String / StringImpl can be expensive if
     // the StringImpl is not already atomic.
     explicit AtomicString(StringImpl* impl) : m_string(add(impl)) { }
-    explicit AtomicString(const String& s) : m_string(add(s.impl())) { }
+    AtomicString(const String& s) : m_string(add(s.impl())) { }
 
     AtomicString(StringImpl* baseString, unsigned start, unsigned length) : m_string(add(baseString, start, length)) { }