Revert of wtf/CheckedArithmetic.h delegates to base/numerics/safe_math.h.

third_party/WebKit/Source/core/fetch/ImageResource.cpp

Index: third_party/WebKit/Source/core/fetch/ImageResource.cpp
diff --git a/third_party/WebKit/Source/core/fetch/ImageResource.cpp b/third_party/WebKit/Source/core/fetch/ImageResource.cpp
index 7761a918c9f1a013da669214ce55aa0ec69f0449..8e2c9bd2964f75c130dd2e0565b70a89f7861510 100644
--- a/third_party/WebKit/Source/core/fetch/ImageResource.cpp
+++ b/third_party/WebKit/Source/core/fetch/ImageResource.cpp
@@ -36,7 +36,6 @@
 #include "platform/TraceEvent.h"
 #include "platform/graphics/BitmapImage.h"
 #include "public/platform/Platform.h"
-#include "wtf/CheckedNumeric.h"
 #include "wtf/CurrentTime.h"
 #include "wtf/StdLibExtras.h"
 
@@ -382,9 +381,9 @@
     if (!image || image != m_image)
         return;
 
-    CheckedNumeric<intptr_t> signedDecodedSize(decodedSize());
-    signedDecodedSize += delta;
-    setDecodedSize(safeCast<size_t>(signedDecodedSize.ValueOrDie()));
+    // TODO(bsep): Crash on underflow, which is possible if an error causes
+    // decodedSize to be 0.
+    setDecodedSize(decodedSize() + delta);
 }
 
 void ImageResource::didDraw(const blink::Image* image)