Initial version of external_oes texture support and unit test

src/gpu/glsl/GrGLSLFragmentShaderBuilder.h

Index: src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
diff --git a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
index 924e3110dfddc217d2260679aa2021d83c82eada..e8746878eb4a01b0b476cc83491747a58bc297ca 100644
--- a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
+++ b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
@@ -33,6 +33,7 @@ public:
      */
     enum GLSLFeature {
         kStandardDerivatives_GLSLFeature = 0,
+        kExternalSampler_GLSLFeature = 1,

[egdaniel, 2015/11/20 21:57:43]

is this public feature enum needed?

[bsalomon, 2015/11/20 22:43:55]

Done.

         kLastGLSLFeature = kStandardDerivatives_GLSLFeature
     };
 
@@ -172,6 +173,7 @@ private:
         kFragCoordConventions_GLSLPrivateFeature = kLastGLSLFeature + 1,
         kBlendEquationAdvanced_GLSLPrivateFeature,
         kBlendFuncExtended_GLSLPrivateFeature,
+        kExternalTexture_GLSLPrivateFeature,
         kLastGLSLPrivateFeature = kBlendFuncExtended_GLSLPrivateFeature
     };