Fix: Reset is_concealed_ in ThreadedImageDecoderProxy::Resume()

[msolianko]

ThreadedImageDecoderProxy::Conceal() sets is_concealed_ = true, which causes Finish() to silently return without posting the decode-complete task to the load thread. This flag was never reset, so after any Blur→Conceal→Freeze→Unfreeze→Resume lifecycle cycle, all existing image loaders would permanently fail to complete — Loader::LoadComplete() would never be called and the image would never display.

The fix resets is_concealed_ to false in Resume() before re-initializing the underlying ImageDecoder, restoring normal Finish() behavior for loaders that survive a conceal/resume cycle.

[github-actions]

🤖 Gemini Suggested Commit Message

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cobalt: Fix image loader after conceal/resume

The ThreadedImageDecoderProxy::is_concealed_ flag was not reset in
Resume() after being set to true by Conceal(). This prevented Finish()
from posting the decode-complete task, causing image loaders to
permanently fail to display images after a conceal/resume cycle.

Reset the is_concealed_ flag in Resume() to restore normal decode
completion and ensure images display correctly.

Bug: 9218

---

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[gemini-code-assist]

Code Review

This pull request correctly fixes a bug where image loaders would fail after a conceal/resume cycle by resetting the is_concealed_ flag. The fix is logical and well-implemented. I have provided one suggestion to further improve the code by using std::atomic<bool> for the flag, which would simplify the thread synchronization logic and be slightly more performant.

[gemini-code-assist]

For a simple boolean flag like is_concealed_, using std::atomic<bool> is generally more efficient and can lead to simpler code than using a base::Lock. This avoids the overhead of lock acquisition and release.

If you change is_concealed_ to be a std::atomic<bool> and remove conceal_lock_, this entire block can be simplified to a single atomic store. This would also require updating other accesses to is_concealed_ (e.g., in Conceal() and Finish()) to use atomic operations instead of the lock.

  is_concealed_ = false;