Correct data size argument type in resource loading path to unsigned

Source/core/fetch/ResourceLoader.cpp

Index: Source/core/fetch/ResourceLoader.cpp
diff --git a/Source/core/fetch/ResourceLoader.cpp b/Source/core/fetch/ResourceLoader.cpp
index 512b3b94d3abde41fda463484c88f3cc989e9958..654c1feab3ba42da8b2c3d9cfe7ddac67c9df857 100644
--- a/Source/core/fetch/ResourceLoader.cpp
+++ b/Source/core/fetch/ResourceLoader.cpp
@@ -437,6 +437,7 @@ void ResourceLoader::didReceiveData(blink::WebURLLoader*, const char* data, int
     m_host->didReceiveData(m_resource, data, length, encodedDataLength);
     if (m_state == Terminated)
         return;
+    RELEASE_ASSERT(length >= 0);
     m_resource->appendData(data, length);
 }