Revert of Roll chromium_revision 7a8b621535..962dfbcdb2 (449940:450031) (patchset #1 id:1 of https://codereview.webrtc.org/2694773003/ )

Reason for revert:
The libvpx roll broke an internal project

Original issue's description:
> Roll chromium_revision 7a8b621535..962dfbcdb2 (449940:450031)
>
> Change log: https://chromium.googlesource.com/chromium/src/+log/7a8b621535..962dfbcdb2
> Full diff: https://chromium.googlesource.com/chromium/src/+/7a8b621535..962dfbcdb2
>
> Changed dependencies:
> * src/base: https://chromium.googlesource.com/chromium/src/base/+log/da9ea7c196..e7ee554267
> * src/build: https://chromium.googlesource.com/chromium/src/build/+log/3e5cfce8cf..11f5df6e25
> * src/ios: https://chromium.googlesource.com/chromium/src/ios/+log/aef3d8defa..ba6815a36f
> * src/third_party: https://chromium.googlesource.com/chromium/src/third_party/+log/a2296b7dbc..26d563eb01
> * src/third_party/libvpx/source/libvpx: https://chromium.googlesource.com/webm/libvpx.git/+log/164db8278f..91f87e7513
> * src/tools: https://chromium.googlesource.com/chromium/src/tools/+log/8bbd3624b9..aceeebe907
> DEPS diff: https://chromium.googlesource.com/chromium/src/+/7a8b621535..962dfbcdb2/DEPS
>
> No update to Clang.
>
> TBR=marpan@webrtc.org,
> BUG=None
>
> Review-Url: https://codereview.webrtc.org/2694773003
> Cr-Commit-Position: refs/heads/master@{#16590}
> Committed: https://chromium.googlesource.com/external/webrtc/+/9c9d95b2dcf6007de99ad640e2f0f48e69dcb9db

TBR=marpan@webrtc.org,buildbot@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=None

Review-Url: https://codereview.webrtc.org/2690243002
Cr-Commit-Position: refs/heads/master@{#16592}