add missing #include <memory>

It's coming through SkRefCnt.h incidentally today.

Change-Id: If729712090749f323c176217add7ebec5bf4cf07
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1773401
Commit-Queue: Mike Klein <mtklein@chromium.org>
Commit-Queue: Philip Rogers <pdr@chromium.org>
Auto-Submit: Mike Klein <mtklein@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#690819}

third_party/blink/public/platform/web_image_generator.h

@@ -31,6 +31,8 @@
 #ifndef THIRD_PARTY_BLINK_PUBLIC_PLATFORM_WEB_IMAGE_GENERATOR_H_
 #define THIRD_PARTY_BLINK_PUBLIC_PLATFORM_WEB_IMAGE_GENERATOR_H_
 
+#include <memory>
+
 #include "third_party/blink/public/platform/web_common.h"
 #include "third_party/skia/include/core/SkRefCnt.h"