clean up pre-storage in canvas

BUG=skia:
TBR=

Review URL: https://codereview.chromium.org/1117213003
diff --git a/src/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index c87c6c5..80e913d 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -530,9 +530,9 @@
     fMCRec = (MCRec*)fMCStack.push_back();
     new (fMCRec) MCRec(fConservativeRasterClip);
 
-    SkASSERT(sizeof(DeviceCM) <= sizeof(fBaseLayerStorage));
-    fMCRec->fLayer = (DeviceCM*)fBaseLayerStorage;
-    new (fBaseLayerStorage) DeviceCM(NULL, NULL, NULL, fConservativeRasterClip, false);
+    SkASSERT(sizeof(DeviceCM) <= sizeof(fDeviceCMStorage));
+    fMCRec->fLayer = (DeviceCM*)fDeviceCMStorage;
+    new (fDeviceCMStorage) DeviceCM(NULL, NULL, NULL, fConservativeRasterClip, false);
 
     fMCRec->fTopLayer = fMCRec->fLayer;
 
@@ -1106,7 +1106,7 @@
             SkDELETE(layer);
         } else {
             // we're at the root
-            SkASSERT(layer == (void*)fBaseLayerStorage);
+            SkASSERT(layer == (void*)fDeviceCMStorage);
             layer->~DeviceCM();
         }
     }