[M145] [dawn][blink] Update callback mode for external texture handling.

Original change's description:
> [dawn][blink] Update callback mode for external texture handling.
> 
> - In https://chromium-review.googlesource.com/c/7080760 we updated
>   all of Blink's callbacks to use AllowProcessEvents instead of
>   AllowSpontaneous because we (1) added a new lock, and (2) needed
>   to ensure that the callbacks run on the "main" thread, not the
>   IO thread. This instance of the callback mode was accidentally
>   not updated resulting in the deadlock bug.
> 
> Bug: 480184158
> Change-Id: I2e4d81c2f4bf5695164b5fe006ce56e73a470471
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7540985
> Reviewed-by: Kai Ninomiya <kainino@chromium.org>
> Commit-Queue: Kai Ninomiya <kainino@chromium.org>
> Commit-Queue: Loko Kung <lokokung@google.com>
> Auto-Submit: Loko Kung <lokokung@google.com>
> Cr-Commit-Position: refs/heads/main@{#1579168}

(cherry picked from commit df11d457424f24db6b1c8f75fa0197a0bf30bab2)

(cherry picked from commit 1c6755b0d8bca46c0f3601081b3a5c09fb880c18)

Bug: 481765255,480184158
Change-Id: I2e4d81c2f4bf5695164b5fe006ce56e73a470471
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7549223
Auto-Submit: Chrome Cherry Picker <chrome-cherry-picker@chops-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Original-Commit-Position: refs/branch-heads/7632@{#1985}
Cr-Original-Branched-From: 0bbdf2913883391365383b0a5dfe7bf9fd1a5213-refs/heads/main@{#1568190}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7571316
Owners-Override: Srinivas Sista <srinivassista@chromium.org>
Cr-Commit-Position: refs/branch-heads/7632_45@{#14}
Cr-Branched-From: 7ad2aeb6be38786b2bf653d667d3df01e68d3c40-refs/branch-heads/7632@{#1825}
Cr-Branched-From: 0bbdf2913883391365383b0a5dfe7bf9fd1a5213-refs/heads/main@{#1568190}