Reland "Flip enable_skia_wuffs_gif gn arg default to true"

This is a reland of f93e096413

With https://skia-review.googlesource.com/c/skia/+/414417 landed in Skia
and rolled into Chromium, crbug.com/1213633 is fixed even with this
change.

Original change's description:
> Flip enable_skia_wuffs_gif gn arg default to true
>
> The gif-animated-partial-load.html web test examines the intermediate
> rendering of loading a GIF image over a simulated slow network
> connection - an incomplete image.
>
> The GIF spec (https://www.w3.org/Graphics/GIF/spec-gif89a.txt) describes
> how to decode a complete GIF file, but does not mention intermediate
> on-screen state. Different decoders have leeway to present different
> partial decodings.
>
> Specifically, Chromium's old decoder only output complete rows of pixels
> and consumed only complete blocks of data. Chromium's new decoder can
> output partial rows and consume partial blocks. (A GIF image's
> compressed pixel data is framed into a sequence of blocks. Each block
> has a length byte, then up to 255 bytes of payload.)
>
> For interlaced GIFs, the old and new decoders also take different
> approaches as to how to expand 'tall' rows: whether the explicit row is
> the center or the top of the strip of implied rows.
>
> To repeat, different (spec-compliant) GIF decoders can produce different
> partial decodings. The Blink web test does a pixel-exact comparison to a
> golden screenshot, so this commit also updates that screenshot.
>
> https://bugs.chromium.org/p/chromium/issues/detail?id=1014044#c3 shows
> the old and new screenshots.
>
> Bug: 1014044
> Change-Id: Ic3038147f3ef83bb0a20c9018b9b4ec44662d3e8
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2639056
> Reviewed-by: Leon Scroggins <scroggo@google.com>
> Commit-Queue: Nigel Tao <nigeltao@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#846698}

Bug: 1014044
Bug: 1214134
Bug: 1213633
Change-Id: If5a1d4ccb14bc63bac9bb8b52f35dd51dfcafb80
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2940044
Reviewed-by: Nigel Tao <nigeltao@chromium.org>
Commit-Queue: Leon Scroggins <scroggo@google.com>
Cr-Commit-Position: refs/heads/master@{#890239}

skia/BUILD.gn

@@ -28,7 +28,7 @@ skia_support_pdf = !is_ios && enable_basic_printing
 skia_support_skottie = true
 
 declare_args() {
-  enable_skia_wuffs_gif = false
+  enable_skia_wuffs_gif = true
 }
 
 # Generate a buildflag header for compile-time checking of Dawn support.

third_party/wuffs/config.gni

@@ -3,5 +3,5 @@
 # found in the LICENSE file.
 
 declare_args() {
-  use_wuffs_gif_parser = false
+  use_wuffs_gif_parser = true
 }