Simplify canvas calls in SkDocument_PDF

As suggested by reed@ in http://crrev.com/711133002

TBR=reed@google.com

Review URL: https://codereview.chromium.org/707533003

src/doc/SkDocument_PDF.cpp

@@ -44,8 +44,8 @@ protected:
             fDevice->setRasterDpi(fRasterDpi);
         }
         fCanvas = SkNEW_ARGS(SkCanvas, (fDevice));
+        fCanvas->clipRect(trimBox);
         fCanvas->translate(trimBox.x(), trimBox.y());
-        fCanvas->clipRect(SkRect::MakeWH(trimBox.width(), trimBox.height()));
         return fCanvas;
     }