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}

modules/video_coding/decoding_state.cc

@@ -297,7 +297,7 @@ bool VCMDecodingState::UsingFlexibleMode(const VCMFrameBuffer* frame) const {
       frame->CodecSpecific()->codecSpecific.VP9.flexible_mode;
   if (is_flexible_mode && frame->PictureId() == kNoPictureId) {
     RTC_LOG(LS_WARNING) << "Frame is marked as using flexible mode but no"
-                        << "picture id is set.";
+                           "picture id is set.";
     return false;
   }
   return is_flexible_mode;