Add GrGLSLShaderBuilder::declareGlobal

BUG=skia:

Change-Id: I75eeb7cbd1bf157c463e5e80b4560a953b7883e8
Reviewed-on: https://skia-review.googlesource.com/8245
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
2 files changed