Encode the Last-Event-ID header in EventSource as UTF-8.

Source/core/page/EventSource.cpp

 /*
  * Copyright (C) 2009, 2012 Ericsson AB. All rights reserved.
  * Copyright (C) 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2011, Code Aurora Forum. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above copyright
@@ skipping 109 matching lines @@
     ASSERT(m_state == CONNECTING);
     ASSERT(!m_requestInFlight);
     ASSERT(executionContext());
 
     ExecutionContext& executionContext = *this->executionContext();
     ResourceRequest request(m_url);
     request.setHTTPMethod("GET");
     request.setHTTPHeaderField("Accept", "text/event-stream");
     request.setHTTPHeaderField("Cache-Control", "no-cache");
     request.setRequestContext(WebURLRequest::RequestContextEventSource);
-    if (!m_lastEventId.isEmpty())
-        request.setHTTPHeaderField("Last-Event-ID", m_lastEventId);
+    if (!m_lastEventId.isEmpty()) {
+        // HTTP headers are Latin-1 byte strings, but the Last-Event-ID header is encoded as UTF-8.
+        // TODO(davidben): This should be captured in the type of setHTTPHeaderField's arguments.
+        CString lastEventIdUtf8 = m_lastEventId.utf8();
+        request.setHTTPHeaderField("Last-Event-ID", AtomicString(reinterpret_cast<const LChar*>(lastEventIdUtf8.data()), lastEventIdUtf8.length()));
+    }
 
     SecurityOrigin* origin = executionContext.securityOrigin();
 
     ThreadableLoaderOptions options;
     options.preflightPolicy = PreventPreflight;
     options.crossOriginRequestPolicy = UseAccessControl;
     options.contentSecurityPolicyEnforcement = ContentSecurityPolicy::shouldBypassMainWorld(&executionContext) ? DoNotEnforceContentSecurityPolicy : EnforceConnectSrcDirective;
 
     ResourceLoaderOptions resourceLoaderOptions;
     resourceLoaderOptions.allowCredentials = (origin->canRequestNoSuborigin(m_url) || m_withCredentials) ? AllowStoredCredentials : DoNotAllowStoredCredentials;
@@ skipping 303 matching lines @@
     return event.release();
 }
 
 DEFINE_TRACE(EventSource)
 {
     RefCountedGarbageCollectedEventTargetWithInlineData::trace(visitor);
     ActiveDOMObject::trace(visitor);
 }
 
 } // namespace blink