Align SkSL const rules more closely with GLSL

This adds Analysis::IsConstantExpression, to determine if an expression
is a constant-expression. It now expands to cover 'const' local and
global variables, because we also enforce that the initializer on those
variables is - in turn - a constant expression.

This fixes 10837 - previously you could initialize a const variable with
a non-constant expression, and we'd emit GLSL that contained that same
pattern, which would fail to compile at the driver level. That should
not be possible any longer.

Bug: skia:10679
Bug: skia:10837
Change-Id: I517820ef4da57fff45768c0b04c55aebc18d3272
Reviewed-by: John Stiles <>
Commit-Queue: Brian Osman <>
12 files changed