Add isSingleComponent bool to getConstantColorComponent

Initial step to allowing effects to use/output 1 or 4 color/coverage components. This cl doesn't change any current logic and all effects still assume they are working with 4 components.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/3b8af078281a5a20f951b9fd84f38d92b8f6217b

Review URL: https://codereview.chromium.org/608253002
47 files changed