Initial version of external_oes texture support and unit test

src/gpu/glsl/GrGLSLCaps.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "GrGLSLCaps.h"
 
@@ skipping 10 matching lines @@
     fBindlessTextureSupport = false;
     fUsesPrecisionModifiers = false;
     fCanUseAnyFunctionInShader = true;
     fForceHighPrecisionNDSTransform = false;
     fCanUseMinAndAbsTogether = true;
     fMustForceNegatedAtanParamToFloat = false;
     fVersionDeclString = nullptr;
     fShaderDerivativeExtensionString = nullptr;
     fFragCoordConventionsExtensionString = nullptr;
     fSecondaryOutputExtensionString = nullptr;
+    fExternalTextureExtensionString = nullptr;
     fFBFetchColorName = nullptr;
     fFBFetchExtensionString = nullptr;
     fAdvBlendEqInteraction = kNotSupported_AdvBlendEqInteraction;
 
     fMustSwizzleInShader = false;
     memset(fConfigSwizzle, 0, sizeof(fConfigSwizzle));
 }
 
 SkString GrGLSLCaps::dump() const {
     SkString r = INHERITED::dump();
@@ skipping 26 matching lines @@
               kAdvBlendEqInteractionStr[fAdvBlendEqInteraction]);
     return r;
 }
 
 void GrGLSLCaps::onApplyOptionsOverrides(const GrContextOptions& options) {
     if (options.fUseShaderSwizzling) {
         fMustSwizzleInShader = true;
     }
 }