Quickly fix the double to SkScalar issue

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2060823004

Review-Url: https://codereview.chromium.org/2060823004
diff --git a/tools/viewer/Viewer.cpp b/tools/viewer/Viewer.cpp
index 465a7aa..48d2c41 100644
--- a/tools/viewer/Viewer.cpp
+++ b/tools/viewer/Viewer.cpp
@@ -350,7 +350,7 @@
         SkRect contentRect = fWindow->getContentRect();
         // If inSplitScreen, translate the image half screen to the right.
         // Thus we have two copies of the image on each half of the screen.
-        contentRect.fLeft += inSplitScreen ? (contentRect.fRight - contentRect.fLeft) * 0.5 : 0;
+        contentRect.fLeft += inSplitScreen ? (contentRect.fRight - contentRect.fLeft) * 0.5f : 0f;
         canvas->clipRect(contentRect);
         canvas->translate(contentRect.fLeft, contentRect.fTop);
     }