With MPArch, a WebContents could have different main frames at different times. Chromium change: https://chromium.googlesource.com/chromium/src/+/2e35a87fa58fbb9f84b9e7b4ffd6e7a9f394f2b3 commit 2e35a87fa58fbb9f84b9e7b4ffd6e7a9f394f2b3 Author: Dave Tapuska <dtapuska@chromium.org> Date: Wed Jun 15 16:45:59 2022 +0000 Remove WebContents::GetMainFrame. Reland 1522398b4b6f6d353cbbbe2aa23ee6c3bdf50dbd with one additional test fixed. This change previously landed but was reverted due to a test being added while this change was in the CQ. All usages have been rewritten to GetPrimaryMainFrame. Remove the deprecated API. BUG=1250404