Enable ASSERT when DCHECK_ALWAYS_ON is defined.

Enable ASSERT when DCHECK_ALWAYS_ON is defined.

It is burdensome to build in debug to check ASSERT. Chromium already has
DCHECK_ALWAYS_ON macro to turn on DCHECK even in release build. Blink also
enables ASSERT when DCHECK_ALWAYS_ON is defined.

[abarth-chromium, 2013-12-03 16:59:10]

not lgtm

DCHECK_ALWAYS_ON is a Chromium concept that Blink should remain ignorant of.

[dshwang, 2013-12-03 17:07:59]

On 2013/12/03 16:59:10, abarth wrote:
> not lgtm
> 
> DCHECK_ALWAYS_ON is a Chromium concept that Blink should remain ignorant of.

Thank you for review.
I was hesitated because Blink supposed to not know DCHECK_ALWAYS_ON. I see.

I have improved idea.
If DCHECK_ALWAYS_ON is defined, define ASSERTIONS_DISABLED_DEFAULT in gyp,
probably blink.gyp. How do you think?

[dshwang, 2013-12-03 19:02:29]

I have investigated more, and I give up it, because so many ASSERT use variables
under NDEBUG guard.

for example,
in WeakPtr.h

#ifndef NDEBUG
        m_boundThread = currentThread();
#endif
  ...
  ASSERT(m_boundThread == currentThread());