Mac: clang build

gpu/command_buffer/client/fenced_allocator.h

Index: gpu/command_buffer/client/fenced_allocator.h
diff --git a/gpu/command_buffer/client/fenced_allocator.h b/gpu/command_buffer/client/fenced_allocator.h
index fb97e37062df63d183fe376a1f521f716ac72e90..fd162db410159ea626d41831051d714a58c28dc4 100644
--- a/gpu/command_buffer/client/fenced_allocator.h
+++ b/gpu/command_buffer/client/fenced_allocator.h
@@ -212,7 +212,9 @@ class FencedAllocatorWrapper {
   // Gets the offset to a memory block given the base memory and the address.
   // It translates NULL to FencedAllocator::kInvalidOffset.
   FencedAllocator::Offset GetOffset(void *pointer) {
-    return pointer ? static_cast<char *>(pointer) - static_cast<char *>(base_) :
+    return pointer ?
+        static_cast<FencedAllocator::Offset>(
+            static_cast<char*>(pointer) - static_cast<char*>(base_)) :
         FencedAllocator::kInvalidOffset;
   }