Revert of Revert of Move DstCopy on gpu into the GrXferProcessor.

src/gpu/GrXferProcessor.cpp

Index: src/gpu/GrXferProcessor.cpp
diff --git a/src/gpu/GrXferProcessor.cpp b/src/gpu/GrXferProcessor.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..e98ae407a8458b993785c7a613e32817e86ead47
--- /dev/null
+++ b/src/gpu/GrXferProcessor.cpp
@@ -0,0 +1,58 @@
+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "GrXferProcessor.h"
+#include "gl/GrGLCaps.h"
+
+GrXferProcessor::GrXferProcessor() : fWillReadDstColor(false), fDstCopyTextureOffset() {
+}
+
+GrXferProcessor::GrXferProcessor(const GrDeviceCoordTexture* dstCopy, bool willReadDstColor)
+    : fWillReadDstColor(willReadDstColor)
+    , fDstCopyTextureOffset() {
+    if (dstCopy && dstCopy->texture()) {
+        fDstCopy.reset(dstCopy->texture());
+        fDstCopyTextureOffset = dstCopy->offset();
+        this->addTextureAccess(&fDstCopy);
+    }
+}
+
+void GrXferProcessor::getGLProcessorKey(const GrGLCaps& caps, GrProcessorKeyBuilder* b) const {
+    uint32_t key = this->willReadDstColor() ? 0x1 : 0x0;
+    if (this->getDstCopyTexture() &&
+        kTopLeft_GrSurfaceOrigin == this->getDstCopyTexture()->origin()) {
+        key |= 0x2;
+    }
+    b->add32(key);
+    this->onGetGLProcessorKey(caps, b);
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+GrXferProcessor* GrXPFactory::createXferProcessor(const GrProcOptInfo& colorPOI,
+                                                  const GrProcOptInfo& coveragePOI,
+                                                  const GrDeviceCoordTexture* dstCopy,
+                                                  const GrDrawTargetCaps& caps) const {
+#ifdef SK_DEBUG
+    if (this->willReadDstColor()) {
+        if (!caps.dstReadInShaderSupport()) {
+            SkASSERT(dstCopy && dstCopy->texture());
+        } else {
+            SkASSERT(!dstCopy || !dstCopy->texture()); 
+        }
+    } else {
+        SkASSERT(!dstCopy || !dstCopy->texture()); 
+
+    }
+#endif
+    return this->onCreateXferProcessor(colorPOI, coveragePOI, dstCopy);
+}
+
+bool GrXPFactory::willNeedDstCopy(const GrDrawTargetCaps& caps) const {
+    return (this->willReadDstColor() && !caps.dstReadInShaderSupport());
+}
+