Implement GL support for buffer textures

src/gpu/glsl/GrGLSLProgramBuilder.cpp

Index: src/gpu/glsl/GrGLSLProgramBuilder.cpp
diff --git a/src/gpu/glsl/GrGLSLProgramBuilder.cpp b/src/gpu/glsl/GrGLSLProgramBuilder.cpp
index 83b50ad534a8cf4f6a89608a851b34502219d92c..5275f6e32834ef4372c9f775394595632d9a3b1b 100644
--- a/src/gpu/glsl/GrGLSLProgramBuilder.cpp
+++ b/src/gpu/glsl/GrGLSLProgramBuilder.cpp
@@ -240,6 +240,12 @@ void GrGLSLProgramBuilder::emitSamplers(const GrProcessor& processor,
             this->addFeature(visibility,
                              1 << GrGLSLShaderBuilder::kExternalTexture_GLSLPrivateFeature,
                              externalFeatureString);
+        } else if (kSamplerBuffer_GrSLType == samplerType) {
+            if (const char* extension = this->glslCaps()->bufferTextureExtensionString()) {
+                this->addFeature(visibility,
+                                 1 << GrGLSLShaderBuilder::kBufferTexture_GLSLPrivateFeature,
+                                 extension);
+            }
         }
         name.printf("Sampler%d", t);
         localSamplerUniforms[t] = this->uniformHandler()->addUniform(access.getVisibility(),