Concatenate string literals at compile time.

This CL was generated by running:
git ls-files | grep ".cc" | xargs perl -i -ne 'BEGIN {undef $/}; s/("[\s\n]*<<[\s\n]*")/" "/g; print;'; git cl format

After that I manually edited modules/audio_processing/gain_controller2.cc to preserve its original
formatting.

This primary benefit of this change is a small reduction in binary size.

Bug: None
Change-Id: I689fa7ba9c717c314bb167e5d592c3c4e0871e29
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/165961
Reviewed-by: Alessio Bazzica <alessiob@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Jonas Olsson <jonasolsson@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30251}

stats/rtc_stats.cc

@@ -99,9 +99,13 @@ bool RTCStats::operator!=(const RTCStats& other) const {
 
 std::string RTCStats::ToJson() const {
   rtc::StringBuilder sb;
-  sb << "{\"type\":\"" << type() << "\","
-     << "\"id\":\"" << id_ << "\","
-     << "\"timestamp\":" << timestamp_us_;
+  sb << "{\"type\":\"" << type()
+     << "\","
+        "\"id\":\""
+     << id_
+     << "\","
+        "\"timestamp\":"
+     << timestamp_us_;
   for (const RTCStatsMemberInterface* member : Members()) {
     if (member->is_defined()) {
       sb << ",\"" << member->name() << "\":";