[LayoutNG] Fix paint/invalidation/selection/selection-change-in-iframe-with-relative-parent.html

This patch cancels selection painting if the NGPaintFragment has no selection
rect.
This happens when we select the last line break but it is not painted whether
it is selected or not anyway.
The test was virtually passed image expectation
but PaintUnderInvalidationChecking has made crash for above reason.

Bug: 708452
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng;luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_layout_ng;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: Ia1939c02aa6327f3dd7620920ec6b60a6b74b790
Reviewed-on: https://chromium-review.googlesource.com/1096592
Commit-Queue: Yoichi Osato <yoichio@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#566790}

third_party/WebKit/LayoutTests/flag-specific/enable-blink-features=LayoutNG/paint/invalidation/selection/selection-change-in-iframe-with-relative-parent-expected.txt

+{
+  "layers": [
+    {
+      "name": "LayoutView #document",
+      "bounds": [800, 600],
+      "drawsContent": false,
+      "backgroundColor": "#FFFFFF"
+    },
+    {
+      "name": "Scrolling Layer",
+      "bounds": [800, 600],
+      "drawsContent": false
+    },
+    {
+      "name": "Scrolling Contents Layer",
+      "bounds": [800, 600],
+      "contentsOpaque": true,
+      "backgroundColor": "#FFFFFF",
+      "paintInvalidations": [
+        {
+          "object": "NGPaintFragment",
+          "rect": [18, 238, 40, 10],
+          "reason": "selection"
+        },
+        {
+          "object": "NGPaintFragment",
+          "rect": [18, 218, 30, 10],
+          "reason": "selection"
+        },
+        {
+          "object": "NGPaintFragment",
+          "rect": [18, 198, 30, 10],
+          "reason": "selection"
+        },
+        {
+          "object": "NGPaintFragment",
+          "rect": [58, 238, 10, 10],
+          "reason": "appeared"
+        },
+        {
+          "object": "NGPaintFragment",
+          "rect": [48, 218, 10, 10],
+          "reason": "appeared"
+        },
+        {
+          "object": "NGPaintFragment",
+          "rect": [48, 198, 10, 10],
+          "reason": "appeared"
+        },
+        {
+          "object": "NGPaintFragment",
+          "rect": [18, 228, 10, 10],
+          "reason": "appeared"
+        },
+        {
+          "object": "NGPaintFragment",
+          "rect": [18, 208, 10, 10],
+          "reason": "appeared"
+        }
+      ]
+    }
+  ],
+  "objectPaintInvalidations": [
+    {
+      "object": "NGPaintFragment",
+      "reason": "selection"
+    },
+    {
+      "object": "NGPaintFragment",
+      "reason": "selection"
+    },
+    {
+      "object": "NGPaintFragment",
+      "reason": "selection"
+    },
+    {
+      "object": "NGPaintFragment",
+      "reason": "selection"
+    },
+    {
+      "object": "NGPaintFragment",
+      "reason": "selection"
+    },
+    {
+      "object": "NGPaintFragment",
+      "reason": "selection"
+    },
+    {
+      "object": "NGPaintFragment",
+      "reason": "selection"
+    },
+    {
+      "object": "NGPaintFragment",
+      "reason": "selection"
+    }
+  ]
+}
+

third_party/blink/renderer/core/paint/ng/ng_text_fragment_painter.cc

@@ -203,6 +203,8 @@ static void PaintSelection(GraphicsContext& context,
 
   const NGPhysicalOffsetRect selection_rect =
       paint_fragment.ComputeLocalSelectionRect(selection_status);
+  if (selection_rect.size.IsEmpty())
+    return;
   const NGPhysicalOffsetRect global_rect(
       selection_rect.offset + NGPhysicalOffset(box_rect.Location()),
       selection_rect.size);