Revert of Move DstCopy on gpu into the GrXferProcessor.

src/gpu/gl/builders/GrGLFragmentShaderBuilder.cpp

Index: src/gpu/gl/builders/GrGLFragmentShaderBuilder.cpp
diff --git a/src/gpu/gl/builders/GrGLFragmentShaderBuilder.cpp b/src/gpu/gl/builders/GrGLFragmentShaderBuilder.cpp
index 86c622d45686693b8ec25df5a705db14a00b45d8..61932f3084bbd290b301b50a0b1f2cc3ccab4590 100644
--- a/src/gpu/gl/builders/GrGLFragmentShaderBuilder.cpp
+++ b/src/gpu/gl/builders/GrGLFragmentShaderBuilder.cpp
@@ -179,9 +179,56 @@
             fbFetchColorName = declared_color_output_name();
         }
         return fbFetchColorName;
+    } else if (fProgramBuilder->fUniformHandles.fDstCopySamplerUni.isValid()) {
+        return kDstCopyColorName;
     } else {
-        return kDstCopyColorName;
-    } 
+        return "";
+    }
+}
+
+void GrGLFragmentShaderBuilder::emitCodeToReadDstTexture() {
+    bool topDown = SkToBool(kTopLeftOrigin_DstReadKeyBit & fProgramBuilder->header().fDstReadKey);
+    const char* dstCopyTopLeftName;
+    const char* dstCopyCoordScaleName;
+    const char* dstCopySamplerName;
+    uint32_t configMask;
+    if (SkToBool(kUseAlphaConfig_DstReadKeyBit & fProgramBuilder->header().fDstReadKey)) {
+        configMask = kA_GrColorComponentFlag;
+    } else {
+        configMask = kRGBA_GrColorComponentFlags;
+    }
+    fProgramBuilder->fUniformHandles.fDstCopySamplerUni =
+            fProgramBuilder->addUniform(GrGLProgramBuilder::kFragment_Visibility,
+                                        kSampler2D_GrSLType,
+                                        kDefault_GrSLPrecision,
+                                        "DstCopySampler",
+                                        &dstCopySamplerName);
+    fProgramBuilder->fUniformHandles.fDstCopyTopLeftUni =
+            fProgramBuilder->addUniform(GrGLProgramBuilder::kFragment_Visibility,
+                                        kVec2f_GrSLType,
+                                        kDefault_GrSLPrecision,
+                                        "DstCopyUpperLeft",
+                                        &dstCopyTopLeftName);
+    fProgramBuilder->fUniformHandles.fDstCopyScaleUni =
+            fProgramBuilder->addUniform(GrGLProgramBuilder::kFragment_Visibility,
+                                        kVec2f_GrSLType,
+                                        kDefault_GrSLPrecision,
+                                        "DstCopyCoordScale",
+                                        &dstCopyCoordScaleName);
+    const char* fragPos = this->fragmentPosition();
+
+    this->codeAppend("// Read color from copy of the destination.\n");
+    this->codeAppendf("vec2 _dstTexCoord = (%s.xy - %s) * %s;",
+                      fragPos, dstCopyTopLeftName, dstCopyCoordScaleName);
+    if (!topDown) {
+        this->codeAppend("_dstTexCoord.y = 1.0 - _dstTexCoord.y;");
+    }
+    this->codeAppendf("vec4 %s = ", GrGLFragmentShaderBuilder::kDstCopyColorName);
+    this->appendTextureLookup(dstCopySamplerName,
+                              "_dstTexCoord",
+                              configMask,
+                              "rgba");
+    this->codeAppend(";");
 }
 
 void GrGLFragmentShaderBuilder::enableCustomOutput() {