Fix SkCanvas::wouldOverwriteEntireSurface() contains test

R=reed@google.com,robertphillips@google.com,bsalomon@google.com

Review URL: https://codereview.chromium.org/1244093005
diff --git a/src/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index 5704358..f55ca5e 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -70,7 +70,7 @@
 
         SkRect devRect;
         this->getTotalMatrix().mapRect(&devRect, *rect);
-        if (devRect.contains(bounds)) {
+        if (!devRect.contains(bounds)) {
             return false;
         }
     }