Initial version of external_oes texture support and unit test

src/gpu/gl/builders/GrGLProgramBuilder.cpp

Index: src/gpu/gl/builders/GrGLProgramBuilder.cpp
diff --git a/src/gpu/gl/builders/GrGLProgramBuilder.cpp b/src/gpu/gl/builders/GrGLProgramBuilder.cpp
index 0ae4f961015a273dc8152258e1e6a3f46df4e323..b5108a74d0fcfb7abe188e6d38575ba7b07f5370 100644
--- a/src/gpu/gl/builders/GrGLProgramBuilder.cpp
+++ b/src/gpu/gl/builders/GrGLProgramBuilder.cpp
@@ -319,6 +319,16 @@ void GrGLProgramBuilder::verify(const GrFragmentProcessor& fp) {
     SkASSERT(fFS.hasReadFragmentPosition() == fp.willReadFragmentPosition());
 }
 
+static GrSLType get_sampler_type(const GrTextureAccess& access) {
+    GrGLTexture* glTexture = static_cast<GrGLTexture*>(access.getTexture());
+    if (glTexture->target() == GR_GL_TEXTURE_EXTERNAL) {
+        return kSamplerExternal_GrSLType;
+    } else {
+        SkASSERT(glTexture->target() == GR_GL_TEXTURE_2D);
+        return kSampler2D_GrSLType;
+    }
+}
+
 template <class Proc>
 void GrGLProgramBuilder::emitSamplers(const GrProcessor& processor,
                                       GrGLSLTextureSampler::TextureSamplerArray* outSamplers,
@@ -329,11 +339,19 @@ void GrGLProgramBuilder::emitSamplers(const GrProcessor& processor,
     SkString name;
     for (int t = 0; t < numTextures; ++t) {
         name.printf("Sampler%d", t);
+        GrSLType samplerType = get_sampler_type(processor.textureAccess(t));
         localSamplerUniforms[t] = this->addUniform(GrGLProgramBuilder::kFragment_Visibility,
-                                                   kSampler2D_GrSLType, kDefault_GrSLPrecision,
+                                                   samplerType, kDefault_GrSLPrecision,
                                                    name.c_str());
         SkNEW_APPEND_TO_TARRAY(outSamplers, GrGLSLTextureSampler,
                                (localSamplerUniforms[t], processor.textureAccess(t)));
+        if (kSamplerExternal_GrSLType == samplerType) {
+            const char* externalFeatureString = this->glslCaps()->externalTextureExtensionString();
+            // We shouldn't ever create a GrGLTexture that requires external sampler type 
+            SkASSERT(externalFeatureString);
+            fFS.addFeature(1 << GrGLSLFragmentShaderBuilder::kExternalTexture_GLSLPrivateFeature,
+                           externalFeatureString);
+        }
     }
 }