private void ensurePromptTokensDetailsIsMutable() {
        if (!((bitField0_ & 0x00000010) != 0)) {
          promptTokensDetails_ =
              new java.util.ArrayList<com.google.cloud.vertexai.api.ModalityTokenCount>(
                  promptTokensDetails_);
          bitField0_ |= 0x00000010;
        }
      }
<pre>
Output only. Number of tokens in the cached part in the input (the cached
content).
</pre>

<code>int32 cached_content_token_count = 5 [(.google.api.field_behavior) = OUTPUT_ONLY];
</code>

@return This builder for chaining.
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/GenerateContentResponse.java