Fix more warnings on linux

Source/core/platform/graphics/chromium/ImageDecodingStore.cpp

Index: Source/core/platform/graphics/chromium/ImageDecodingStore.cpp
diff --git a/Source/core/platform/graphics/chromium/ImageDecodingStore.cpp b/Source/core/platform/graphics/chromium/ImageDecodingStore.cpp
index d79a78f29228ce1460af9bf88d6d5e8dde6c1db3..f8744b3241e77b93776ba10be814eb017cc90965 100644
--- a/Source/core/platform/graphics/chromium/ImageDecodingStore.cpp
+++ b/Source/core/platform/graphics/chromium/ImageDecodingStore.cpp
@@ -263,19 +263,19 @@ size_t ImageDecodingStore::memoryUsageInBytes()
     return m_memoryUsageInBytes;
 }
 
-unsigned ImageDecodingStore::cacheEntries()
+int ImageDecodingStore::cacheEntries()
 {
     MutexLocker lock(m_mutex);
     return m_imageCacheMap.size() + m_decoderCacheMap.size();
 }
 
-unsigned ImageDecodingStore::imageCacheEntries()
+int ImageDecodingStore::imageCacheEntries()
 {
     MutexLocker lock(m_mutex);
     return m_imageCacheMap.size();
 }
 
-unsigned ImageDecodingStore::decoderCacheEntries()
+int ImageDecodingStore::decoderCacheEntries()
 {
     MutexLocker lock(m_mutex);
     return m_decoderCacheMap.size();