Use presence of a content key as non-scratch indicator

BUG=skia:2889

Committed: https://skia.googlesource.com/skia/+/9eefe0851eeaa8ded05b4774ebcb38ed201d5dbf

Review URL: https://codereview.chromium.org/639873002
Remove tab parameter from GrGLSLMulVarBy4f function

With pretty printing of shader code, there is no longer a need to explictily
have tabs in our code.

BUG=skia:

Review URL: https://codereview.chromium.org/648463002
Whitespace change to test CQ's trybots

(SkipBuildbotRuns)
TBR=
BUG=skia:

Review URL: https://codereview.chromium.org/646663002