Use skia.mojom.BitmapN32 in BackgroundFetch mojoms

These bitmaps are safer for transport from untrustworthy sources since
all bitmaps should be in N32 format and the browser can make bad
assumptions as a result.

R=dcheng@chromium.org

Bug: 1144462
Change-Id: I36cbfe48f61964797095aa07b0ee03a60fd39897
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2572642Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#833953}

third_party/blink/public/mojom/background_fetch/background_fetch.mojom

@@ -131,7 +131,7 @@ interface BackgroundFetchService {
         string developer_id,
         array<FetchAPIRequest> requests,
         BackgroundFetchOptions options,
-        skia.mojom.BitmapWithArbitraryBpp? icon,
+        skia.mojom.BitmapN32? icon,
         BackgroundFetchUkmData ukm_data)
       => (BackgroundFetchError error,
           BackgroundFetchRegistration? registration);
@@ -157,7 +157,7 @@ interface BackgroundFetchService {
 interface BackgroundFetchRegistrationService {
   // Updates the user interface for the Background Fetch registration.
   UpdateUI(string? title,
-           skia.mojom.BitmapWithArbitraryBpp? icon)
+           skia.mojom.BitmapN32? icon)
       => (BackgroundFetchError error);
 
   // Aborts the Background Fetch registration.