Add wrapBackendTextureAsRenderTarget API

src/image/SkSurface_Gpu.cpp

Index: src/image/SkSurface_Gpu.cpp
diff --git a/src/image/SkSurface_Gpu.cpp b/src/image/SkSurface_Gpu.cpp
index 24ac6d33124b82a237f3bfffd6a07d25bcdb8e64..07d6f24dd30e3af23b69a3bc27776e3810e2581a 100644
--- a/src/image/SkSurface_Gpu.cpp
+++ b/src/image/SkSurface_Gpu.cpp
@@ -7,6 +7,7 @@
 
 #include "SkSurface_Gpu.h"
 
+#include "GrResourceProvider.h"
 #include "SkCanvas.h"
 #include "SkGpuDevice.h"
 #include "SkImage_Base.h"
@@ -108,6 +109,10 @@ void SkSurface_Gpu::onDiscard() {
     fDevice->accessRenderTarget()->discard();
 }
 
+void SkSurface_Gpu::onPrepareForExternalIO() {
+    fDevice->accessRenderTarget()->prepareForExternalIO();
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 SkSurface* SkSurface::NewRenderTargetDirect(GrRenderTarget* target, const SkSurfaceProps* props) {
@@ -170,4 +175,23 @@ SkSurface* SkSurface::NewFromBackendRenderTarget(GrContext* context,
     return new SkSurface_Gpu(device);
 }
 
+SkSurface* SkSurface::NewFromBackendTextureAsRenderTarget(GrContext* context,
+                                                          const GrBackendTextureDesc& desc,
+                                                          const SkSurfaceProps* props) {
+    if (nullptr == context) {
+        return nullptr;
+    }
+    SkAutoTUnref<GrRenderTarget> rt(
+            context->resourceProvider()->wrapBackendTextureAsRenderTarget(desc));
+    if (!rt) {
+        return nullptr;
+    }
+    SkAutoTUnref<SkGpuDevice> device(SkGpuDevice::Create(rt, props,
+                                                         SkGpuDevice::kUninit_InitContents));
+    if (!device) {
+        return nullptr;
+    }
+    return new SkSurface_Gpu(device);
+}
+
 #endif