cc: use viewport-wide tiles for GPU rasterization.

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 85249812d5fbc9d5ea119537e014ae5e80eb80b2..94c3d201639d0dd90a29545ba18ca067f43edd8a 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -573,6 +573,13 @@ gfx::Size PictureLayerImpl::CalculateTileSize(
       layer_tree_impl()->resource_provider()->max_texture_size();
 
   gfx::Size default_tile_size = layer_tree_impl()->settings().default_tile_size;
+  if (ShouldUseGpuRasterization()) {
+    // TODO(ernstm) crbug.com/365877: We need a unified way to override the
+    // default-tile-size.
+    default_tile_size =
+        gfx::Size(layer_tree_impl()->device_viewport_size().width(),
+                  layer_tree_impl()->device_viewport_size().height() / 4);
+  }
   default_tile_size.SetToMin(gfx::Size(max_texture_size, max_texture_size));
 
   gfx::Size max_untiled_content_size =
@@ -593,10 +600,12 @@ gfx::Size PictureLayerImpl::CalculateTileSize(
   // 500x500 max untiled size would get 500x12 tiles.  Also do this
   // if the layer is small.
   if (any_dimension_one_tile || !any_dimension_too_large) {
-    int width =
-        std::min(max_untiled_content_size.width(), content_bounds.width());
-    int height =
-        std::min(max_untiled_content_size.height(), content_bounds.height());
+    int width = std::min(
+        std::max(max_untiled_content_size.width(), default_tile_size.width()),
+        content_bounds.width());
+    int height = std::min(
+        std::max(max_untiled_content_size.height(), default_tile_size.height()),
+        content_bounds.height());
     // Round width and height up to the closest multiple of 64, or 56 if
     // we should avoid power-of-two textures. This helps reduce the number
     // of different textures sizes to help recycling, and also keeps all