Change the context type name to "bitmaprender" for ImageBitmapRenderingContext
Previously, we used "imagebitmap". Firefox uses "bitmaprenderer". This
changes makes the two interoperable. This will be relfected in the
spec which is WIP.
BUG=
597767
Committed:
https://crrev.com/3d30be906486920495089f6e63f2ea8c1869726f
Cr-Commit-Position: refs/heads/master@{#383781}