Add gl_SampleMask functionality to fragment builders

src/gpu/glsl/GrGLSL.h

Index: src/gpu/glsl/GrGLSL.h
diff --git a/src/gpu/glsl/GrGLSL.h b/src/gpu/glsl/GrGLSL.h
index 6fc8f83c7a3ca1be80fada8a9ef72a12d923ca02..1fe23107d88cc283f3747e50c2f17b2a6414707e 100644
--- a/src/gpu/glsl/GrGLSL.h
+++ b/src/gpu/glsl/GrGLSL.h
@@ -37,9 +37,17 @@ enum GrGLSLGeneration {
      */
     k330_GrGLSLGeneration,
     /**
+     * Desktop GLSL 4.00
+     */
+    k400_GrGLSLGeneration,
+    /**
      * ES GLSL 3.10 only TODO Make GLSLCap objects to make this more granular
      */
     k310es_GrGLSLGeneration,
+    /**
+     * ES GLSL 3.20
+     */
+    k320es_GrGLSLGeneration,
 };
 
 bool GrGLSLSupportsNamedFragmentShaderOutputs(GrGLSLGeneration);
@@ -112,6 +120,20 @@ static inline const char* GrGLSLTypeString(GrSLType t) {
     }
 }
 
+/**
+ * Returns the minimum precision that can fully represent an int with the provided number of bits.
+ */
+static inline GrSLPrecision GrGLSLIntMinPrecisionForNBits(int bits) {

[bsalomon, 2016/02/12 20:58:17]

If we're not using this can we remove it?

[Chris Dalton, 2016/02/12 21:01:50]

Oops. Done.

+    SkASSERT(bits <= 32);
+    if (bits <= 9) { // Lowp integers are spec'd to have at least 9 bits.
+        return kLow_GrSLPrecision;
+    } else if (bits <= 16) {
+        return kMedium_GrSLPrecision;
+    } else {
+        return kHigh_GrSLPrecision;
+    }
+}
+
 /** A generic base-class representing a GLSL expression.
  * The instance can be a variable name, expression or vecN(0) or vecN(1). Does simple constant
  * folding with help of 1 and 0.