Support foo.{r,g,b,a}, where foo is a float4.

Change-Id: I68e9c36406db77bd0025c33cdbfc55324fa40568
Merge commit 'ec29bc0265b0a67e7e47947fd5e0707f46c15d4a' into oxygen_1006

* commit 'ec29bc0265b0a67e7e47947fd5e0707f46c15d4a':
  Support foo.{r,g,b,a}, where foo is a float4.