Make not-reusing-scratch-textures only apply to texture uploads

src/gpu/GrSWMaskHelper.cpp

Index: src/gpu/GrSWMaskHelper.cpp
===================================================================
--- src/gpu/GrSWMaskHelper.cpp	(revision 12025)
+++ src/gpu/GrSWMaskHelper.cpp	(working copy)
@@ -138,6 +138,9 @@
     // writing since no one else will be using 'texture'
     bool reuseScratch = fContext->getGpu()->caps()->reuseScratchTextures();
 
+    // Since we're uploading to it, 'texture' shouldn't have a render target.
+    SkASSERT(NULL == texture->asRenderTarget());
+
     texture->writePixels(0, 0, fBM.width(), fBM.height(),
                          kAlpha_8_GrPixelConfig,
                          fBM.getPixels(), fBM.rowBytes(),