Ensure line-break is on correct object if trailing collapsed whitespace pushes us over line-end

A follow-up to https://codereview.chromium.org/2479333002.

Bug: 641334
Change-Id: If0e92b89422b3f9406d5f8d10fec2d90f83f0e06
Reviewed-on: https://chromium-review.googlesource.com/573500
Commit-Queue: Emil A Eklund <eae@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488076}

third_party/WebKit/LayoutTests/fast/block/float/assert-when-moving-float-2-expected.txt

+fooPass if no assert in debug.

third_party/WebKit/LayoutTests/fast/block/float/assert-when-moving-float-2.html

+<div style="width: 5px;">
+  <img id="makeTaller" style="height: 50px; width: 1px"><img id="removeThis" style="width: 5px; height: 5px;"> <div style="float: left;">foo</div>Pass if no assert in debug.</div>
+<script>
+if (window.testRunner)
+    testRunner.dumpAsText();
+var removeThis = document.getElementById("removeThis");
+removeThis.offsetTop;
+removeThis.parentNode.removeChild(removeThis); 
+;
+makeTaller.style.height = '55px';
+</script>

third_party/WebKit/Source/core/layout/line/BreakingContextInlineHeaders.h

@@ -1516,8 +1516,13 @@ inline void BreakingContext::CommitAndUpdateLineBreakIfNeeded() {
         current_style_->CollapseWhiteSpace())
       trailing_objects_.Clear();
 
-    if (!width_.FitsOnLine() && width_.FitsOnLine(0, kExcludeWhitespace) &&
-        ignoring_spaces_ && next_object_) {
+    // If we are going to break before a float on an object that is just
+    // collapsible white space then make sure the line break is moved to
+    // the float.
+    if (width_.FitsOnLine(0, kExcludeWhitespace) && next_object_ &&
+        next_object_.IsFloating() && current_.GetLineLayoutItem().IsText() &&
+        LineLayoutText(current_.GetLineLayoutItem())
+            .IsAllCollapsibleWhitespace()) {
       width_.Commit();
       line_break_.MoveToStartOf(next_object_);
     }