Add gl_SampleMask functionality to fragment builders

src/gpu/glsl/GrGLSLShaderBuilder.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrSwizzle.h"
 #include "glsl/GrGLSLShaderBuilder.h"
 #include "glsl/GrGLSLCaps.h"
@@ skipping 94 matching lines @@
 
 void GrGLSLShaderBuilder::appendTextureLookupAndModulate(const char* modulation,
                                                          const GrGLSLTextureSampler& sampler,
                                                          const char* coordName,
                                                          GrSLType varyingType) {
     SkString lookup;
     this->appendTextureLookup(&lookup, sampler, coordName, varyingType);
     this->codeAppend((GrGLSLExpr4(modulation) * GrGLSLExpr4(lookup)).c_str());
 }
 
-void GrGLSLShaderBuilder::addFeature(uint32_t featureBit, const char* extensionName) {
-    if (!(featureBit & fFeaturesAddedMask)) {
-        this->extensions().appendf("#extension %s: require\n", extensionName);
-        fFeaturesAddedMask |= featureBit;
+bool GrGLSLShaderBuilder::addFeature(uint32_t featureBit, const char* extensionName) {
+    if (featureBit & fFeaturesAddedMask) {
+        return false;
     }
+    this->extensions().appendf("#extension %s: require\n", extensionName);
+    fFeaturesAddedMask |= featureBit;
+    return true;
 }
 
 void GrGLSLShaderBuilder::appendDecls(const VarArray& vars, SkString* out) const {
     for (int i = 0; i < vars.count(); ++i) {
         vars[i].appendDecl(fProgramBuilder->glslCaps(), out);
         out->append(";\n");
     }
 }
 
 void GrGLSLShaderBuilder::addLayoutQualifier(const char* param, InterfaceQualifier interface) {
@@ skipping 36 matching lines @@
     this->code().append("}");
 
     for (int i = 0; i <= fCodeIndex; i++) {
         fCompilerStrings[i] = fShaderStrings[i].c_str();
         fCompilerStringLengths[i] = (int)fShaderStrings[i].size();
     }
 
     fFinalized = true;
 }