Use texture size to determine precision of texture coord varyings

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 24 matching lines @@
     };
 
     enum Precision {
         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,
+
+        kLast_Precision = kHigh_Precision
     };
+    static const int kPrecisionCount = kLast_Precision + 1;
 
     /**
      * Defaults to a float with no precision specifier
      */
     GrShaderVar()
         : fType(kFloat_GrSLType)
         , fTypeModifier(kNone_TypeModifier)
         , fCount(kNonArray)
         , fPrecision(kDefault_Precision) {
     }
@@ skipping 167 matching lines @@
 
 protected:
     GrSLType        fType;
     TypeModifier    fTypeModifier;
     SkString        fName;
     int             fCount;
     Precision       fPrecision;
 };
 
 #endif