Roll src/third_party/libavif/src/ 01ee4caa5..50c5bbd8f (16 commits)

https://chromium.googlesource.com/external/github.com/AOMediaCodec/libavif.git/+log/01ee4caa5ab5..50c5bbd8f04a

$ git log 01ee4caa5..50c5bbd8f --date=short --no-merges --format='%ad %ae %s'
2020-08-05 jdrago Minor changelog tweak
2020-08-05 jdrago Fix incorrect 16-to-8 monochrome YUV conversion
2020-08-03 kornel Make decoding optional
2020-08-03 linkmauve Add an ignoreAlpha field to avifRGBImage
2020-07-28 dnovomesky Save support in gdk-pixbuf component
2020-07-31 jdrago Update changelog
2020-07-31 jdrago Only ever create one iref box, filled with multiple cdsc boxes
2020-07-24 asn cmake: Include avif INTERFACE_INCLUDE_DIRECTORIES first
2020-07-22 asn cmake: Use correct include dir for apps/shared
2020-07-22 dnovomesky Fix a crash in the gdk-pixbuf loader, removed unnecessary asserts
2020-07-21 ccom CMake: Add -Wno-error=c11-extensions for dav1d
2020-07-19 ccom CMake: Set C standard to c99
2020-07-19 ccom CMake: Only enable CXX if using libgav1
2020-07-16 wtc Move ptrU8,ptrV8,ptrU16,ptrV16 out of i for loop
2020-07-17 linkmauve Fix a crash in the gdk-pixbuf loader when error is NULL
2020-07-19 jdrago Disable libgav1 until abseil-cpp stops using CMP0077 on newer CMake versions

Created with:
  roll-dep src/third_party/libavif/src
R=dalecurtis@chromium.org

Change-Id: I2b93528963d3a56802a40a8f788f6158e247b726
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2340070
Commit-Queue: Wan-Teh Chang <wtc@google.com>
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#795332}

DEPS

@@ -342,7 +342,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling libavif
   # and whatever else without interference from each other.
-  'libavif_revision': '01ee4caa5ab52b2f6f3e500fd3a0f70e0099b031',
+  'libavif_revision': '50c5bbd8f04ae9d8dc98556745b44476c3ce3223',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling nearby
   # and whatever else without interference from each other.