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>
diff --git a/src/gpu/glsl/GrGLSLShaderBuilder.h b/src/gpu/glsl/GrGLSLShaderBuilder.h
index 983d50b..2d6aaf0 100644
--- a/src/gpu/glsl/GrGLSLShaderBuilder.h
+++ b/src/gpu/glsl/GrGLSLShaderBuilder.h
@@ -102,6 +102,8 @@
        this->definitions().append(";\n");
     }
 
+    void declareGlobal(const GrShaderVar&);
+
     /**
     * Called by GrGLSLProcessors to add code to one of the shaders.
     */