clean up default precision handling

include/gpu/GrShaderVar.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrShaderVar_DEFINED
 #define GrShaderVar_DEFINED
 
@@ skipping 17 matching lines @@
         kIn_TypeModifier,
         kInOut_TypeModifier,
         kUniform_TypeModifier,
         // GL Specific types below
         kAttribute_TypeModifier,
         kVaryingIn_TypeModifier,
         kVaryingOut_TypeModifier
     };
 
     enum Precision {
-        kLow_Precision,         // lowp
-        kMedium_Precision,      // mediump
-        kHigh_Precision,        // highp
-        kDefault_Precision,     // Default for the current context. We make
-                                // fragment shaders default to mediump on ES2
-                                // because highp support is not guaranteed (and
-                                // we haven't been motivated to test for it).
-                                // Otherwise, highp.
+        kLow_Precision,
+        kMedium_Precision,
+        kHigh_Precision,
+
+        // Default precision is medium. This is because on OpenGL ES 2 highp support is not
+        // guaranteed. On (non-ES) OpenGL the specifiers have no effect on precision.
+        kDefault_Precision = kMedium_Precision,
     };
 
     /**
      * Defaults to a float with no precision specifier
      */
     GrShaderVar()
         : fType(kFloat_GrSLType)
         , fTypeModifier(kNone_TypeModifier)
         , fCount(kNonArray)
         , fPrecision(kDefault_Precision) {
@@ skipping 168 matching lines @@
 
 protected:
     GrSLType        fType;
     TypeModifier    fTypeModifier;
     SkString        fName;
     int             fCount;
     Precision       fPrecision;
 };
 
 #endif