cc: add rasterize time to continuous painting graph data in impl-side-painting

cc/ring_buffer.h

Index: cc/ring_buffer.h
diff --git a/cc/ring_buffer.h b/cc/ring_buffer.h
index 929d74cb0e91e2d28e861c77a8bce375eea8794d..5e015fe3f8604bf48283c622f3e781afd6ce73f4 100644
--- a/cc/ring_buffer.h
+++ b/cc/ring_buffer.h
@@ -36,11 +36,20 @@ class RingBuffer {
     return buffer_[BufferIndex(n)];
   }
 
-  void SaveToBuffer(T value) {
+  T& MutableReadBuffer(size_t n) {
+    DCHECK(IsFilledIndex(n));
+    return buffer_[BufferIndex(n)];
+  }
+
+  void SaveToBuffer(const T& value) {
     buffer_[BufferIndex(0)] = value;
     current_index_++;
   }
 
+  void Clear() {
+    current_index_ = 0;
+  }
+
  private:
   inline size_t BufferIndex(size_t n) const {
     return (current_index_ + n) % size;