Update from chromium https://crrev.com/304586

Review URL: https://codereview.chromium.org/732423002
diff --git a/cc/debug/ring_buffer.h b/cc/debug/ring_buffer.h
index 94d8459..f9a6749 100644
--- a/cc/debug/ring_buffer.h
+++ b/cc/debug/ring_buffer.h
@@ -12,9 +12,7 @@
 template<typename T, size_t kSize>
 class RingBuffer {
  public:
-  explicit RingBuffer()
-    : current_index_(0) {
-  }
+  RingBuffer() : current_index_(0) {}
 
   size_t BufferSize() const {
     return kSize;