Remove GrSurfaceProxy::desc()

Adds a numStencilSamples() getter.

Bug: skia:
Change-Id: I1e57f19b3cb490a6214ea436622ed8128a5a9303
Reviewed-on: https://skia-review.googlesource.com/16994
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
diff --git a/src/gpu/gl/GrGLCaps.cpp b/src/gpu/gl/GrGLCaps.cpp
index 49274d7..977670d 100644
--- a/src/gpu/gl/GrGLCaps.cpp
+++ b/src/gpu/gl/GrGLCaps.cpp
@@ -2125,7 +2125,8 @@
     }
 
     {
-        bool srcIsMSAARenderbuffer = src->desc().fSampleCnt > 0 && this->usesMSAARenderBuffers();
+        bool srcIsMSAARenderbuffer = GrFSAAType::kUnifiedMSAA == src->fsaaType() &&
+                                     this->usesMSAARenderBuffers();
         if (srcIsMSAARenderbuffer) {
             // It's illegal to call CopyTexSubImage2D on a MSAA renderbuffer. Set up for FBO
             // blit or fail.