Use the single char overload of append() when possible.

third_party/WebKit/Source/modules/mediasource/SourceBuffer.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 67 matching lines @@
         MediaSource::logAndThrowDOMException(exceptionState, InvalidStateError, "This SourceBuffer is still processing an 'appendBuffer', 'appendStream', or 'remove' operation.");
         return true;
     }
 
     return false;
 }
 
 WTF::String webTimeRangesToString(const WebTimeRanges& ranges)
 {
     StringBuilder stringBuilder;
-    stringBuilder.append("{");
+    stringBuilder.append('{');
     for (auto& r : ranges) {
         stringBuilder.append(" [");
         stringBuilder.appendNumber(r.start);
-        stringBuilder.append(";");
+        stringBuilder.append(';');
         stringBuilder.appendNumber(r.end);
-        stringBuilder.append("]");
+        stringBuilder.append(']');
     }
     stringBuilder.append(" }");
     return stringBuilder.toString();
 }
 
 } // namespace
 
 SourceBuffer* SourceBuffer::create(std::unique_ptr<WebSourceBuffer> webSourceBuffer, MediaSource* source, GenericEventQueue* asyncEventQueue)
 {
     SourceBuffer* sourceBuffer = new SourceBuffer(std::move(webSourceBuffer), source, asyncEventQueue);
@@ skipping 1154 matching lines @@
     visitor->trace(m_removeAsyncPartRunner);
     visitor->trace(m_appendStreamAsyncPartRunner);
     visitor->trace(m_stream);
     visitor->trace(m_audioTracks);
     visitor->trace(m_videoTracks);
     EventTargetWithInlineData::trace(visitor);
     ActiveDOMObject::trace(visitor);
 }
 
 } // namespace blink