DocumentLoader: simplify CommitData

- Merge data_buffer_ and committed_data_buffer_.
- Simplify blocked parser logic.

Reentrancy protection now accounts for any possible code path
leading to appending bytes to the parser: CommitData changes protection
flag in_commit_data_, while its only caller ProcessBufferData checks
the flag.

Bug: none
Change-Id: I1b019bf43ab73b0ebc3855169fd8ef075c911e9e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1830068
Reviewed-by: Nate Chapin <japhet@chromium.org>
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701379}
2 files changed