Fix crash caused by DCHECK global pointer for --single-process model

Fix crash caused by DCHECK global pointer for --single-process model

DCHECK for these three global pointers is not suitable for --single-process
model, since they are created when RenderThread created and all RenderThreads
under --single-process model are created in the same process (Browser Process).

In this patch we will remove these three DCHECK.

BUG=462848

[jinlong.zhai, 2015-02-28 10:24:50]

jinlong.zhai@samsung.com changed reviewers:
+ jrummell@chromium.org, sandersd@chromium.org

[jinlong.zhai, 2015-02-28 10:24:51]

hi,
  These crash happens when running Debug/chrome.
  Please take a look at.

thanks,
Jinlong

[jrummell, 2015-03-02 23:54:14]

jrummell@chromium.org changed reviewers:
+ tommi@chromium.org

[jrummell, 2015-03-02 23:54:14]

+tommi@, who looks like the person that added these DCHECKs and may understand
the code better.

https://codereview.chromium.org/969553002/diff/1/content/renderer/media/aec_d...
File content/renderer/media/aec_dump_message_filter.cc (right):

https://codereview.chromium.org/969553002/diff/1/content/renderer/media/aec_d...
content/renderer/media/aec_dump_message_filter.cc:32: DCHECK_EQ(g_filter, this);
If the DCHECK in the constructor needs to be removed, why aren't these? I would
assume that if there is 2 creations, then one of the these would fail.

[jinlong.zhai, 2015-03-06 07:19:53]

On 2015/03/02 23:54:14, jrummell wrote:
> +tommi@, who looks like the person that added these DCHECKs and may understand
> the code better.
> 
>
https://codereview.chromium.org/969553002/diff/1/content/renderer/media/aec_d...
> File content/renderer/media/aec_dump_message_filter.cc (right):
> 
>
https://codereview.chromium.org/969553002/diff/1/content/renderer/media/aec_d...
> content/renderer/media/aec_dump_message_filter.cc:32: DCHECK_EQ(g_filter,
this);
> If the DCHECK in the constructor needs to be removed, why aren't these? I
would
> assume that if there is 2 creations, then one of the these would fail.

Fix in patch is not true.
I'm consider another proper way to fix it.