Replace ASSERT by RTC_DCHECK in all non-test code.

Bulk of the changes were produced using

  git grep -l ' ASSERT(' | grep -v test | grep -v 'common\.h' |\
    xargs -n1 sed -i 's/ ASSERT(/ RTC_DCHECK(/'

followed by additional includes of base/checks.h in affected files,
and git cl format.

Also had to do some tweaks to #if !defined(NDEBUG) logic in the
taskrunner code (webrtc/base/task.cc, webrtc/base/taskparent.cc,
webrtc/base/taskparent.h, webrtc/base/taskrunner.cc), replaced to
consistently use RTC_DCHECK_IS_ON, and some of the checks needed
additional #if protection.

Test code was excluded, because it should probably use RTC_CHECK
rather than RTC_DCHECK.

BUG=webrtc:6424

Review-Url: https://codereview.webrtc.org/2620303003
Cr-Commit-Position: refs/heads/master@{#16030}
diff --git a/webrtc/api/peerconnectionfactory.cc b/webrtc/api/peerconnectionfactory.cc
index 9da6e57..32f461e 100644
--- a/webrtc/api/peerconnectionfactory.cc
+++ b/webrtc/api/peerconnectionfactory.cc
@@ -25,6 +25,7 @@
 #include "webrtc/api/videosourceproxy.h"
 #include "webrtc/api/videotrack.h"
 #include "webrtc/base/bind.h"
+#include "webrtc/base/checks.h"
 #include "webrtc/media/engine/webrtcmediaengine.h"
 #include "webrtc/media/engine/webrtcvideodecoderfactory.h"
 #include "webrtc/media/engine/webrtcvideoencoderfactory.h"
@@ -129,7 +130,7 @@
   RTC_DCHECK(signaling_thread);
   // TODO: Currently there is no way creating an external adm in
   // libjingle source tree. So we can 't currently assert if this is NULL.
-  // ASSERT(default_adm != NULL);
+  // RTC_DCHECK(default_adm != NULL);
 }
 
 PeerConnectionFactory::~PeerConnectionFactory() {
@@ -345,7 +346,7 @@
 }
 
 cricket::MediaEngineInterface* PeerConnectionFactory::CreateMediaEngine_w() {
-  ASSERT(worker_thread_ == rtc::Thread::Current());
+  RTC_DCHECK(worker_thread_ == rtc::Thread::Current());
   return cricket::WebRtcMediaEngineFactory::Create(
       default_adm_.get(), audio_decoder_factory_, video_encoder_factory_.get(),
       video_decoder_factory_.get(), external_audio_mixer_);