Make MemoryCache::contains() take a const Resource pointer.

Source/core/fetch/MemoryCache.cpp

Index: Source/core/fetch/MemoryCache.cpp
diff --git a/Source/core/fetch/MemoryCache.cpp b/Source/core/fetch/MemoryCache.cpp
index 4e0d6023a6601d46e792b103183c77e4eb2362d9..7deda544049639131b00ff35e0a4a91cb35e2408 100644
--- a/Source/core/fetch/MemoryCache.cpp
+++ b/Source/core/fetch/MemoryCache.cpp
@@ -124,11 +124,11 @@ void MemoryCache::replace(Resource* newResource, Resource* oldResource)
         insertInLiveDecodedResourcesList(newResource);
 }
 
-bool MemoryCache::contains(Resource* resource)
+bool MemoryCache::contains(const Resource* resource) const
 {
     if (resource->url().isNull())
         return false;
-    MemoryCacheEntry* entry = m_resources.get(resource->url());
+    const MemoryCacheEntry* entry = m_resources.get(resource->url());
     return entry && entry->m_resource == resource;
 }