Reference result if DCHECKs are off.

Replace call to ZX_DLOG_IF(), which won't reference |result| in builds
in which DCHECKs are disabled.

Bug: 852541
TBR: rockot
Change-Id: I0b8ff421a690691277a4f73730f4c756faf5a17e
Reviewed-on: https://chromium-review.googlesource.com/1132488Reviewed-by: Wez <wez@chromium.org>
Reviewed-by: Ken Rockot <rockot@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574070}

mojo/public/cpp/platform/platform_handle.cc

@@ -53,7 +53,8 @@ zx::handle CloneHandle(const zx::handle& handle) {
 
   zx::handle dupe;
   zx_status_t result = handle.duplicate(ZX_RIGHT_SAME_RIGHTS, &dupe);
-  ZX_DLOG_IF(ERROR, result != ZX_OK, result) << "zx_duplicate_handle";
+  if (result != ZX_OK)
+    ZX_DLOG(ERROR, result) << "zx_duplicate_handle";
   return std::move(dupe);
 }
 #elif defined(OS_MACOSX) && !defined(OS_IOS)