Add caps and GL API for buffer texture

src/gpu/glsl/GrGLSLCaps.cpp

Index: src/gpu/glsl/GrGLSLCaps.cpp
diff --git a/src/gpu/glsl/GrGLSLCaps.cpp b/src/gpu/glsl/GrGLSLCaps.cpp
index 189b76675294677dd7fd519a6b9cfc6dfa6d8430..f14274143bd381dc3275195b6184379b28e32bd6 100755
--- a/src/gpu/glsl/GrGLSLCaps.cpp
+++ b/src/gpu/glsl/GrGLSLCaps.cpp
@@ -29,11 +29,13 @@ GrGLSLCaps::GrGLSLCaps(const GrContextOptions& options) {
     fSampleVariablesSupport = false;
     fSampleMaskOverrideCoverageSupport = false;
     fExternalTextureSupport = false;
+    fBufferTextureSupport = false;
     fVersionDeclString = nullptr;
     fShaderDerivativeExtensionString = nullptr;
     fFragCoordConventionsExtensionString = nullptr;
     fSecondaryOutputExtensionString = nullptr;
     fExternalTextureExtensionString = nullptr;
+    fBufferTextureExtensionString = nullptr;
     fNoPerspectiveInterpolationExtensionString = nullptr;
     fMultisampleInterpolationExtensionString = nullptr;
     fSampleVariablesExtensionString = nullptr;
@@ -80,6 +82,7 @@ SkString GrGLSLCaps::dump() const {
     r.appendf("Sample mask override coverage support: %s\n", (fSampleMaskOverrideCoverageSupport ?
                                                               "YES" : "NO"));
     r.appendf("External texture support: %s\n", (fExternalTextureSupport ? "YES" : "NO"));
+    r.appendf("Buffer texture support: %s\n", (fBufferTextureSupport ? "YES" : "NO"));
     r.appendf("Max VS Samplers: %d\n", fMaxVertexSamplers);
     r.appendf("Max GS Samplers: %d\n", fMaxGeometrySamplers);
     r.appendf("Max FS Samplers: %d\n", fMaxFragmentSamplers);