[LayoutNG] Fix caret position resolution when dealing with floats

The current caret position resolution algorithm assumes that all
descendants of an inline formatting context fragments are inline, and
hence contained in a line box. This is not the case with floats and
out-of-flow positioned fragments.

This patch makes the algorithm handle them correctly.

Bug: 808914
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Change-Id: If238323a9b9694fb4a9d1668254a89eea8d6756e
Reviewed-on: https://chromium-review.googlesource.com/902685Reviewed-by: Emil A Eklund <eae@chromium.org>
Reviewed-by: Yoichi Osato <yoichio@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534629}

third_party/WebKit/Source/core/editing/LocalCaretRectTest.cpp

@@ -656,4 +656,35 @@ TEST_P(ParameterizedLocalCaretRectTest, TextAndImageMixedHeight) {
                 {Position(text2, 1), TextAffinity::kDownstream}));
 }
 
+TEST_P(ParameterizedLocalCaretRectTest, FloatFirstLetter) {
+  LoadAhem();
+  InsertStyleElement("#container::first-letter{float:right}");
+  SetBodyContent(
+      "<div id=container style='font: 10px/10px Ahem; width: 40px'>foo</div>");
+  const Node* foo = GetElementById("container")->firstChild();
+  const LayoutObject* first_letter = AssociatedLayoutObjectOf(*foo, 0);
+  const LayoutObject* remaining_text = AssociatedLayoutObjectOf(*foo, 1);
+
+  // TODO(editing-dev): Legacy LocalCaretRectOfPosition() is not aware of the
+  // first-letter LayoutObject. Fix it.
+
+  EXPECT_EQ(
+      LocalCaretRect(LayoutNGEnabled() ? first_letter : remaining_text,
+                     LayoutRect(0, 0, 1, 10)),
+      LocalCaretRectOfPosition({Position(foo, 0), TextAffinity::kDownstream}));
+  EXPECT_EQ(
+      LocalCaretRect(remaining_text,
+                     LayoutRect(LayoutNGEnabled() ? 0 : 10, 0, 1, 10)),
+      LocalCaretRectOfPosition({Position(foo, 1), TextAffinity::kDownstream}));
+  EXPECT_EQ(
+      LocalCaretRect(remaining_text,
+                     LayoutRect(LayoutNGEnabled() ? 10 : 20, 0, 1, 10)),
+      LocalCaretRectOfPosition({Position(foo, 2), TextAffinity::kDownstream}));
+  EXPECT_EQ(
+      LocalCaretRect(remaining_text, LayoutNGEnabled()
+                                         ? LayoutRect(20, 0, 1, 10)
+                                         : LayoutRect()),
+      LocalCaretRectOfPosition({Position(foo, 3), TextAffinity::kDownstream}));
+}
+
 }  // namespace blink

third_party/WebKit/Source/core/layout/ng/inline/ng_caret_rect.cc

@@ -415,8 +415,11 @@ NGCaretPosition ComputeNGCaretPosition(const LayoutBlockFlow& context,
       current_line = ToNGPhysicalLineBoxFragment(child.fragment.get());
     }
 
-    // Every inline fragment should have a line box (inclusive) ancestor.
-    DCHECK(current_line);
+    if (!current_line) {
+      // Floats and out-of-flow positioned children are not in any line box;
+      // they don't have caret positions by their sides, either.
+      continue;
+    }
 
     const CaretPositionResolution resolution =
         TryResolveCaretPositionWithFragment(*child.fragment, *current_line,