Revert "[MediaRecorder] Fix corrupted video problem with pause/resume spamming."

This reverts commit b7dab9dc0c395b471b2c735b0c4de9360f1d7a3c.

Reason for revert: caused crbug.com/1065827 which is more severe.

Original change's description:
> [MediaRecorder] Fix corrupted video problem with pause/resume spamming.
> 
> 
> This CL fixes an issue caused by the following sequence of events:
> 1. MediaRecorderHandler::Pause(): recording_ = false
> 2. MediaRecorderHandler::WriteData(): if (!recording_) return
> 
> The problem is that the WriteData() invocation was decided to
> happen while the recorder was still resumed. In that state, wholes
> would be produced which are not tolerated by vpx_encoder, which
> interprets those as corrupted.
> 
> The fix reverts the semantic of the code to when the class was not under
> oilpan and would require manual memory management and restores the
> "invalidation" semantic from when the class was using a weak ptr.
> In fact, the weak reference would be invalidated hence making the
> callbacks no-ops. To keep the same semantic, this CL introduces a
> boolean and avoids overloading the meaning of 'recording_'
> 
> This should also not require calling Pause() in Stop(), as all callbacks
> will not do anything after Stop() is called.
> 
> Fixed: 1060358
> Change-Id: I88b0aeb10fd13034412f3689648cebd1df40d6bf
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2106072
> Commit-Queue: Armando Miraglia <armax@chromium.org>
> Reviewed-by: Markus Handell <handellm@google.com>
> Cr-Commit-Position: refs/heads/master@{#752838}

TBR=armax@chromium.org,handellm@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: Id8a148253433576469cd7958addf48afdabf44eb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2128070
Reviewed-by: Armando Miraglia <armax@chromium.org>
Commit-Queue: Armando Miraglia <armax@chromium.org>
Cr-Commit-Position: refs/heads/master@{#754872}