Move some of the adding stencil attachment logic of Gpu and into Render Target.

src/gpu/GrGpu.cpp

Index: src/gpu/GrGpu.cpp
diff --git a/src/gpu/GrGpu.cpp b/src/gpu/GrGpu.cpp
index e1b8ed5c8522b54a84df49bbe31fc4b7835fc9a3..51102f4a577e6661c74a0d69425c72f0fe4a479b 100644
--- a/src/gpu/GrGpu.cpp
+++ b/src/gpu/GrGpu.cpp
@@ -134,8 +134,9 @@ GrTexture* GrGpu::createTexture(const GrSurfaceDesc& origDesc, bool budgeted,
     return tex;
 }
 
-bool GrGpu::attachStencilAttachmentToRenderTarget(GrRenderTarget* rt) {
+bool GrGpu::getStencilAttachment(const GrRenderTarget* rt, GrStencilAttachment** stencil) {
     SkASSERT(nullptr == rt->renderTargetPriv().getStencilAttachment());
+    SkASSERT(nullptr == *stencil);
     GrUniqueKey sbKey;
 
     int width = rt->width();
@@ -149,31 +150,17 @@ bool GrGpu::attachStencilAttachmentToRenderTarget(GrRenderTarget* rt) {
 
     GrStencilAttachment::ComputeSharedStencilAttachmentKey(width, height,
         rt->numStencilSamples(), &sbKey);
-    SkAutoTUnref<GrStencilAttachment> sb(static_cast<GrStencilAttachment*>(
-        this->getContext()->getResourceCache()->findAndRefUniqueResource(sbKey)));
-    if (sb) {
-        if (this->attachStencilAttachmentToRenderTarget(sb, rt)) {
-            rt->renderTargetPriv().didAttachStencilAttachment(sb);
-            return true;
-        }
+    *stencil = static_cast<GrStencilAttachment*>(
+        this->getContext()->getResourceCache()->findAndRefUniqueResource(sbKey));
+    if (*stencil) {
         return false;
     }
-    if (this->createStencilAttachmentForRenderTarget(rt, width, height)) {
-        // Right now we're clearing the stencil buffer here after it is
-        // attached to an RT for the first time. When we start matching
-        // stencil buffers with smaller color targets this will no longer
-        // be correct because it won't be guaranteed to clear the entire
-        // sb.
-        // We used to clear down in the GL subclass using a special purpose
-        // FBO. But iOS doesn't allow a stencil-only FBO. It reports unsupported
-        // FBO status.
-        this->clearStencil(rt);
-        GrStencilAttachment* sb = rt->renderTargetPriv().getStencilAttachment();
-        sb->resourcePriv().setUniqueKey(sbKey);
+    *stencil = this->createStencilAttachmentForRenderTarget(rt, width, height);
+    if (*stencil) {
+        (*stencil)->resourcePriv().setUniqueKey(sbKey);
         return true;
-    } else {
-        return false;
     }
+    return false;
 }
 
 GrTexture* GrGpu::wrapBackendTexture(const GrBackendTextureDesc& desc, GrWrapOwnership ownership) {
@@ -184,7 +171,7 @@ GrTexture* GrGpu::wrapBackendTexture(const GrBackendTextureDesc& desc, GrWrapOwn
     }
     // TODO: defer this and attach dynamically
     GrRenderTarget* tgt = tex->asRenderTarget();
-    if (tgt && !this->attachStencilAttachmentToRenderTarget(tgt)) {
+    if (tgt && !tgt->renderTargetPriv().attachStencilAttachment()) {
         tex->unref();
         return nullptr;
     } else {