Make v8AtomicString take a StringView.

third_party/WebKit/Source/bindings/core/v8/WindowProxy.cpp

Index: third_party/WebKit/Source/bindings/core/v8/WindowProxy.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/WindowProxy.cpp b/third_party/WebKit/Source/bindings/core/v8/WindowProxy.cpp
index c6cb29661fc2cab3797a97d98c6bc06d8cc97012..a8d4be011e9c99e2e3dd5ae22c0b877b6ee463d1 100644
--- a/third_party/WebKit/Source/bindings/core/v8/WindowProxy.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/WindowProxy.cpp
@@ -466,10 +466,9 @@ void WindowProxy::setSecurityToken(SecurityOrigin* origin)
         token = frameSecurityToken + token;
     }
 
-    CString utf8Token = token.utf8();

[esprehn, 2016/07/13 00:48:53]

Doing this meant we were allocating an extra temporary string plus we were doing
latin1 -> utf8 -> latin1 here for no reason.

     // NOTE: V8 does identity comparison in fast path, must use a symbol
     // as the security token.
-    context->SetSecurityToken(v8AtomicString(m_isolate, utf8Token.data(), utf8Token.length()));
+    context->SetSecurityToken(v8AtomicString(m_isolate, token));
 }
 
 void WindowProxy::updateDocument()