Mojo: Optimize VerifyUserPointer().

mojo/system/memory.cc

Index: mojo/system/memory.cc
diff --git a/mojo/system/memory.cc b/mojo/system/memory.cc
index df658ae5ee3d405aff88f8f244259583f22f81b3..fe7edef3da3f4a3871171a19f197c65d4e2b70c6 100644
--- a/mojo/system/memory.cc
+++ b/mojo/system/memory.cc
@@ -11,9 +11,9 @@
 namespace mojo {
 namespace system {
 
-bool VerifyUserPointer(const void* pointer, size_t count, size_t size_each) {
-  DCHECK_GT(size_each, 0u);
-  if (count > std::numeric_limits<size_t>::max() / size_each)
+template <size_t size>
+bool VerifyUserPointerForSize(const void* pointer, size_t count) {
+  if (count > std::numeric_limits<size_t>::max() / size)
     return false;
 
   // TODO(vtl): If running in kernel mode, do a full verification. For now, just
@@ -22,5 +22,9 @@ bool VerifyUserPointer(const void* pointer, size_t count, size_t size_each) {
   return count == 0 || !!pointer;
 }
 
+// Explicitly instantiate the sizes we need. Add instantiations as needed.
+template bool VerifyUserPointerForSize<1>(const void*, size_t);
+template bool VerifyUserPointerForSize<4>(const void*, size_t);
+
 }  // namespace system
 }  // namespace mojo