Bug 1254273 - Align the displayport to a max of 256 pixels even if the layer is larger. r=BenWa

MozReview-Commit-ID: CLghUMWkJU8

layout/base/nsLayoutUtils.cpp

@@ -953,8 +953,11 @@ GetDisplayPortFromMarginsData(nsIContent* aContent,
   if (APZCCallbackHelper::IsDisplayportSuppressed()) {
     alignment = ScreenSize(1, 1);
   } else if (gfxPrefs::LayersTilesEnabled()) {
-    alignment = ScreenSize(gfxPlatform::GetPlatform()->GetTileWidth(),
-                           gfxPlatform::GetPlatform()->GetTileHeight());
+    // Don't align to tiles if they are too large, because we could expand
+    // the displayport by a lot which can take more paint time. It's a tradeoff
+    // though because if we don't align to tiles we have more waste on upload.
+    alignment = ScreenSize(std::min(256, gfxPlatform::GetPlatform()->GetTileWidth()),
+                           std::min(256, gfxPlatform::GetPlatform()->GetTileHeight()));
   } else {
     // If we're not drawing with tiles then we need to be careful about not
     // hitting the max texture size and we only need 1 draw call per layer