Make appending default precision be controled by GLSL

src/gpu/glsl/GrGLSL.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrGLSL.h"
+#include "GrGLSLCaps.h"
 #include "SkString.h"
 
 bool GrGLSLSupportsNamedFragmentShaderOutputs(GrGLSLGeneration gen) {
     switch (gen) {
         case k110_GrGLSLGeneration:
             return false;
         case k130_GrGLSLGeneration:
         case k140_GrGLSLGeneration:
         case k150_GrGLSLGeneration:
         case k330_GrGLSLGeneration:
         case k310es_GrGLSLGeneration:
             return true;
     }
     return false;
 }
 
+void GrGLSLAppendDefaultFloatPrecisionDeclaration(GrSLPrecision p,
+                                                  const GrGLSLCaps& glslCaps,
+                                                  SkString* out) {
+    if (glslCaps.usesPrecisionModifiers()) {
+        switch (p) {
+            case kHigh_GrSLPrecision:
+                out->append("precision highp float;\n");
+                break;
+            case kMedium_GrSLPrecision:
+                out->append("precision mediump float;\n");
+                break;
+            case kLow_GrSLPrecision:
+                out->append("precision lowp float;\n");
+                break;
+            default:
+                SkFAIL("Unknown precision value.");
+        }
+    }
+}
+
 void GrGLSLMulVarBy4f(SkString* outAppend, const char* vec4VarName, const GrGLSLExpr4& mulFactor) {
     if (mulFactor.isOnes()) {
         *outAppend = SkString();
     }
 
     if (mulFactor.isZeros()) {
         outAppend->appendf("%s = vec4(0);", vec4VarName);
     } else {
         outAppend->appendf("%s *= %s;", vec4VarName, mulFactor.c_str());
     }
 }