Make previousPositionOf() to handle yet another no previous position case

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

 // Copyright 2015 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 "core/editing/VisibleUnits.h"
 
 #include "core/dom/Text.h"
 #include "core/editing/EditingTestBase.h"
 #include "core/editing/VisiblePosition.h"
 #include "core/html/HTMLTextFormControlElement.h"
@@ skipping 1030 matching lines @@
 
     // In case of each line has one character, VisiblePosition are:
     // [C,Dn]   [C,Up]  [B, Dn]   [B, Up]
     //  A        A       A         A|
     //  B        B|     |B         B
     // |C        C       C         C
     EXPECT_EQ(PositionWithAffinity(Position(sample, 1)), previousPositionOf(createVisiblePosition(Position(sample, 2))).toPositionWithAffinity());
     EXPECT_EQ(PositionWithAffinity(Position(sample, 1)), previousPositionOf(createVisiblePosition(Position(sample, 2), TextAffinity::Upstream)).toPositionWithAffinity());
 }
 
+TEST_F(VisibleUnitsTest, previousPositionOfNoPreviousPosition)
+{
+    setBodyContent(
+        "<span contenteditable='true'>"
+            "<span> </span>"
+            " " // This whitespace causes no previous position.
+            "<div id='anchor'> bar</div>"
+        "</span>");
+    const Position position(document().getElementById("anchor")->firstChild(), 1);
+    EXPECT_EQ(Position(), previousPositionOf(createVisiblePosition(position)).deepEquivalent());
+}
+
 TEST_F(VisibleUnitsTest, rendersInDifferentPositionAfterAnchor)
 {
     const char* bodyContent = "<p id='sample'>00</p>";
     setBodyContent(bodyContent);
     Element* sample = document().getElementById("sample");
 
     EXPECT_FALSE(rendersInDifferentPosition(Position(), Position()));
     EXPECT_FALSE(rendersInDifferentPosition(Position(), Position::afterNode(sample)))
         << "if one of position is null, the reuslt is false.";
     EXPECT_FALSE(rendersInDifferentPosition(Position::afterNode(sample), Position(sample, 1)));
@@ skipping 242 matching lines @@
 {
     // Repro case of crbug.com/584030
     const char* bodyContent = "<button><rt><script>document.designMode = 'on'</script></rt></button>";
     setBodyContent(bodyContent);
 
     Node* button = document().querySelector("button", ASSERT_NO_EXCEPTION);
     EXPECT_TRUE(endsOfNodeAreVisuallyDistinctPositions(button));
 }
 
 } // namespace blink