ImageEncoder: Make implicit cast explicit

- Implicit cast from size_t (uint_64_t) to wtf_size_t (uint_32_t) loses precision. Let's document this and make it clear.

../../third_party/blink/renderer/platform/image-encoders/image_encoder.h:26:48: error: implicit conversion loses integer precision: 'size_t' (aka 'unsigned long') to 'WTF::wtf_size_t' (aka 'unsigned int') [-Werror,-Wshorten-64-to-32]
    dst_->Append((const unsigned char*)buffer, size);
          ~~~~~~                               ^~~~

Bug: 896479
Change-Id: Iadedc5c3c4ed1de57cadcc2783a0eb42d64cbd76
Reviewed-on: https://chromium-review.googlesource.com/c/1409808
Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Commit-Queue: Darwin Huang <huangdarwin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622651}
1 file changed