Add RTC_ prefix to (D)CHECKs and related macros.

We must remove dependency on Chromium, i.e. we can't use Chromium's base/logging.h. That means we need to define these macros in WebRTC also when doing Chromium builds. And this causes redefinition.

Alternative solutions:
* Check if we already have defined e.g. CHECK, and don't define them in that case. This makes us depend on include order in Chromium, which is not acceptable.
* Don't allow using the macros in WebRTC headers. Error prone since if someone adds it there by mistake it may compile fine, but later break if a header in added or order is changed in Chromium. That will be confusing and hard to enforce.
* Ensure that headers that are included by an embedder don't include our macros. This would require some heavy refactoring to be maintainable and enforcable.
* Changes in Chromium for this is obviously not an option.

BUG=chromium:468375
NOTRY=true

Review URL: https://codereview.webrtc.org/1335923002

Cr-Commit-Position: refs/heads/master@{#9964}
diff --git a/webrtc/video/call_perf_tests.cc b/webrtc/video/call_perf_tests.cc
index a301452..bbf4caa 100644
--- a/webrtc/video/call_perf_tests.cc
+++ b/webrtc/video/call_perf_tests.cc
@@ -548,7 +548,7 @@
                                  const PacketTime& packet_time) override {
       VideoSendStream::Stats stats = send_stream_->GetStats();
       if (stats.substreams.size() > 0) {
-        DCHECK_EQ(1u, stats.substreams.size());
+        RTC_DCHECK_EQ(1u, stats.substreams.size());
         int bitrate_kbps =
             stats.substreams.begin()->second.total_bitrate_bps / 1000;
         if (bitrate_kbps > 0) {
@@ -595,7 +595,7 @@
       if (pad_to_min_bitrate_) {
         encoder_config->min_transmit_bitrate_bps = kMinTransmitBitrateBps;
       } else {
-        DCHECK_EQ(0, encoder_config->min_transmit_bitrate_bps);
+        RTC_DCHECK_EQ(0, encoder_config->min_transmit_bitrate_bps);
       }
     }