cc: Set shader id when reading PaintShader

This doesn't really matter, but for consistency we should set this, so
that writing out the PaintShader yields the same PaintShader when
reading it back.  This fixes a fuzzer bug.

Bug: 883217
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I25488ce92fa8259c4be9974d0fdf4422e65b60ac
Reviewed-on: https://chromium-review.googlesource.com/1239544
Commit-Queue: enne <enne@chromium.org>
Commit-Queue: Khushal <khushalsagar@chromium.org>
Reviewed-by: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593410}

cc/paint/paint_op_reader.cc

@@ -463,6 +463,8 @@ void PaintOpReader::Read(sk_sp<PaintShader>* shader) {
     size_t record_size = Read(&ref.record_);
     size_t post_size = options_.transfer_cache->GetTotalEntrySizes();
     shader_size = post_size - pre_size + record_size;
+
+    ref.id_ = shader_id;
   }
   decltype(ref.colors_)::size_type colors_size = 0;
   ReadSize(&colors_size);