Make appending default precision be controled by GLSL

src/gpu/glsl/GrGLSL.cpp

Index: src/gpu/glsl/GrGLSL.cpp
diff --git a/src/gpu/glsl/GrGLSL.cpp b/src/gpu/glsl/GrGLSL.cpp
index c77b7fab20719f3042de5c9376948181ce665246..2de81ddd60efb85bbe1eefdf205454735910bbe0 100644
--- a/src/gpu/glsl/GrGLSL.cpp
+++ b/src/gpu/glsl/GrGLSL.cpp
@@ -6,6 +6,7 @@
  */
 
 #include "GrGLSL.h"
+#include "GrGLSLCaps.h"
 #include "SkString.h"
 
 bool GrGLSLSupportsNamedFragmentShaderOutputs(GrGLSLGeneration gen) {
@@ -22,6 +23,26 @@ bool GrGLSLSupportsNamedFragmentShaderOutputs(GrGLSLGeneration gen) {
     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();