Copy m_namespaceRules when copying StyleSheetContents to avoid crashing.

third_party/WebKit/Source/core/css/StyleRule.cpp

Index: third_party/WebKit/Source/core/css/StyleRule.cpp
diff --git a/third_party/WebKit/Source/core/css/StyleRule.cpp b/third_party/WebKit/Source/core/css/StyleRule.cpp
index b3509de5cc5202a429873a19a198f649d987ea32..55059c8fb6c5a6ec7dc4d539f235b7a05931fc1e 100644
--- a/third_party/WebKit/Source/core/css/StyleRule.cpp
+++ b/third_party/WebKit/Source/core/css/StyleRule.cpp
@@ -150,9 +150,10 @@ StyleRuleBase* StyleRuleBase::copy() const {
       return toStyleRuleKeyframes(this)->copy();
     case Viewport:
       return toStyleRuleViewport(this)->copy();
+    case Namespace:
+      return toStyleRuleNamespace(this)->copy();
     case Charset:
     case Keyframe:
-    case Namespace:
       ASSERT_NOT_REACHED();
       return nullptr;
   }