r358275 had changed the decoding way of the text resource with the progressive decoding in order to avoid merging SharedBuffer segments. However, it looks like that the process time of text decoding was increased. Especially, it increased the launching time when a web app is launched on web runtime based on Chromium.

According to my simple test, r358275 increased about 28ms the processing time in TextResource::DecodedText when loading nytimes.com.

 - With original implementation: 41ms
 - Current implementation: 69ms

- Test scenario.
  1. Download https://www.nytimes.com to local system.
  2. Add a time measure code inside TextResource::DecodedText
  3. Launch Chrome with the downloaded nytimes.com files.
   e.g) ./out/Debug/chrome ~/Nytimes.html