[layoutng] Use the override width even when we're not a flex item

(And also use it for positioned boxes)

We want to use this for layoutng/legacy interop. For legacy layout,
there should be no change in behavior because flexbox is currently
the only caller of this function:
https://cs.chromium.org/search/?q=setOverrideLogicalContentWidth&sq=package:chromium&type=cs

Interestingly, the height version did not have this limitation already.

This patch also deleted an outdated FIXME comment.

R=atotic@chromium.org,eae@chromium.org
BUG=635619

Review-Url: https://codereview.chromium.org/2624143005
Cr-Commit-Position: refs/heads/master@{#443056}

third_party/WebKit/Source/core/layout/LayoutBox.cpp

@@ -2479,22 +2479,19 @@ void LayoutBox::computeLogicalWidth(
   computedValues.m_margins.m_start = marginStart();
   computedValues.m_margins.m_end = marginEnd();
 
-  if (isOutOfFlowPositioned()) {
-    computePositionedLogicalWidth(computedValues);
-    return;
-  }
-
   // The parent box is flexing us, so it has increased or decreased our
   // width.  Use the width from the style context.
-  // FIXME: Account for writing-mode in flexible boxes.
-  // https://bugs.webkit.org/show_bug.cgi?id=46418
-  if (hasOverrideLogicalContentWidth() &&
-      parent()->isFlexibleBoxIncludingDeprecated()) {
+  if (hasOverrideLogicalContentWidth()) {
     computedValues.m_extent =
         overrideLogicalContentWidth() + borderAndPaddingLogicalWidth();
     return;
   }
 
+  if (isOutOfFlowPositioned()) {
+    computePositionedLogicalWidth(computedValues);
+    return;
+  }
+
   // FIXME: Account for writing-mode in flexible boxes.
   // https://bugs.webkit.org/show_bug.cgi?id=46418
   bool inVerticalBox = parent()->isDeprecatedFlexibleBox() &&
@@ -2979,8 +2976,6 @@ void LayoutBox::computeLogicalHeight(
 
     // The parent box is flexing us, so it has increased or decreased our
     // height. We have to grab our cached flexible height.
-    // FIXME: Account for writing-mode in flexible boxes.
-    // https://bugs.webkit.org/show_bug.cgi?id=46418
     if (hasOverrideLogicalContentHeight()) {
       h = Length(overrideLogicalContentHeight(), Fixed);
     } else if (treatAsReplaced) {