Handle large rects better.

cc/trees/layer_tree_host_common_unittest.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_host_common.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <memory>
@@ skipping 1106 matching lines @@
   grand_child->SetDrawsContent(true);
   float device_scale_factor = 1.f;
   float page_scale_factor = 1.f;
   LayerImpl* page_scale_layer = nullptr;
   LayerImpl* inner_viewport_scroll_layer = nullptr;
   LayerImpl* outer_viewport_scroll_layer = nullptr;
   ExecuteCalculateDrawProperties(root, device_scale_factor, page_scale_factor,
                                  page_scale_layer, inner_viewport_scroll_layer,
                                  outer_viewport_scroll_layer);
 
-  // Mapping grand_child's bounds to screen space produces an empty rect so
-  // grand_child should be hidden.
-  EXPECT_EQ(gfx::Rect(), grand_child->visible_layer_rect());
+  // Mapping grand_child's bounds to screen space produces an empty rect, but
+  // only because it is turned sideways.  The entire rect is contained inside
+  // the clip, and is only empty so land as the numerical precision of the

[Peter Mayo, 2017/03/28 20:15:40]

s/land/long/

Done.

+  // transform is effectively perfect.  Currently we do the calculation the
+  // way around, and the Projection of the screen space clip into layer space

[jaydasika, 2017/03/28 20:11:48]

nit : the 'other' way around ?

[Peter Mayo, 2017/03/28 20:15:40]

Done.

+  // includes the entire bounds.
+  EXPECT_EQ(gfx::Rect(grand_child->bounds()),
+            grand_child->visible_layer_rect());
 }
 
 TEST_F(LayerTreeHostCommonTest, TransformsForDegenerateIntermediateLayer) {
   // A layer that is empty in one axis, but not the other, was accidentally
   // skipping a necessary translation.  Without that translation, the coordinate
   // space of the layer's draw transform is incorrect.
   //
   // Normally this isn't a problem, because the layer wouldn't be drawn anyway,
   // but if that layer becomes a render surface, then its draw transform is
   // implicitly inherited by the rest of the subtree, which then is positioned
@@ skipping 9587 matching lines @@
   EXPECT_EQ(scroll_child6.id, grand_child10->scroll_tree_index());
   EXPECT_EQ(scroll_root1.id, parent3->scroll_tree_index());
   EXPECT_EQ(scroll_child7.id, child8->scroll_tree_index());
   EXPECT_EQ(scroll_root1.id, parent4->scroll_tree_index());
   EXPECT_EQ(scroll_root1.id, child9->scroll_tree_index());
   EXPECT_EQ(scroll_root1.id, grand_child12->scroll_tree_index());
 }
 
 }  // namespace
 }  // namespace cc