cc: Handle overflow/underflow in MathUtil::RoundUp/RoundDown functions.

cc/layers/picture_layer_impl.cc

Index: cc/layers/picture_layer_impl.cc
diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index bb1f4c590907246f4bcb8556c17f7a637c0ffb06..e2d0fdb786fdc5de428548665e07ef8773f8595e 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -702,7 +702,8 @@ gfx::Size PictureLayerImpl::CalculateTileSize(
       divisor = 2;
     if (content_bounds.width() <= viewport_width / 4)
       divisor = 1;
-    default_tile_height = MathUtil::RoundUp(viewport_height, divisor) / divisor;
+    default_tile_height =
+        MathUtil::UncheckedRoundUp(viewport_height, divisor) / divisor;
 
     // Grow default sizes to account for overlapping border texels.
     default_tile_width += 2 * PictureLayerTiling::kBorderTexels;
@@ -738,12 +739,12 @@ gfx::Size PictureLayerImpl::CalculateTileSize(
   // Clamp the tile width/height to the content width/height to save space.
   if (content_bounds.width() < default_tile_width) {
     tile_width = std::min(tile_width, content_bounds.width());
-    tile_width = MathUtil::RoundUp(tile_width, kTileRoundUp);
+    tile_width = MathUtil::UncheckedRoundUp(tile_width, kTileRoundUp);
     tile_width = std::min(tile_width, default_tile_width);
   }
   if (content_bounds.height() < default_tile_height) {
     tile_height = std::min(tile_height, content_bounds.height());
-    tile_height = MathUtil::RoundUp(tile_height, kTileRoundUp);
+    tile_height = MathUtil::UncheckedRoundUp(tile_height, kTileRoundUp);
     tile_height = std::min(tile_height, default_tile_height);
   }