Check MayHaveMargin() in BlockAlignment()

This patch avoids to check for "auto" margins
if MayHaveMargin() is true in BlockAlignment().

The patch also modifies the calls to SetMayHaveMargin()
so they are also called for "auto" margins.

BUG=1098231

Change-Id: I400c0c0b92f52ffbd4c0333a27e17e7083c4bae2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2489301Reviewed-by: Koji Ishii <kojii@chromium.org>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Commit-Queue: Manuel Rego <rego@igalia.com>
Cr-Commit-Position: refs/heads/master@{#819955}

third_party/blink/renderer/core/layout/ng/ng_length_utils.cc

@@ -25,12 +25,14 @@ enum class EBlockAlignment { kStart, kCenter, kEnd };
 
 inline EBlockAlignment BlockAlignment(const ComputedStyle& style,
                                       const ComputedStyle& container_style) {
-  bool start_auto = style.MarginStartUsing(container_style).IsAuto();
-  bool end_auto = style.MarginEndUsing(container_style).IsAuto();
-  if (start_auto || end_auto) {
-    if (start_auto)
-      return end_auto ? EBlockAlignment::kCenter : EBlockAlignment::kEnd;
-    return EBlockAlignment::kStart;
+  if (style.MayHaveMargin()) {
+    bool start_auto = style.MarginStartUsing(container_style).IsAuto();
+    bool end_auto = style.MarginEndUsing(container_style).IsAuto();
+    if (start_auto || end_auto) {
+      if (start_auto)
+        return end_auto ? EBlockAlignment::kCenter : EBlockAlignment::kEnd;
+      return EBlockAlignment::kStart;
+    }
   }
 
   // If none of the inline margins are auto, look for -webkit- text-align

third_party/blink/renderer/core/style/computed_style.h

@@ -1514,28 +1514,28 @@ class ComputedStyle : public ComputedStyleBase,
   // Margin utility functions.
   void SetMarginTop(const Length& v) {
     if (MarginTop() != v) {
-      if (!v.IsZero())
+      if (!v.IsZero() || v.IsAuto())
         SetMayHaveMargin();
       MutableMarginTopInternal() = v;
     }
   }
   void SetMarginRight(const Length& v) {
     if (MarginRight() != v) {
-      if (!v.IsZero())
+      if (!v.IsZero() || v.IsAuto())
         SetMayHaveMargin();
       MutableMarginRightInternal() = v;
     }
   }
   void SetMarginBottom(const Length& v) {
     if (MarginBottom() != v) {
-      if (!v.IsZero())
+      if (!v.IsZero() || v.IsAuto())
         SetMayHaveMargin();
       MutableMarginBottomInternal() = v;
     }
   }
   void SetMarginLeft(const Length& v) {
     if (MarginLeft() != v) {
-      if (!v.IsZero())
+      if (!v.IsZero() || v.IsAuto())
         SetMayHaveMargin();
       MutableMarginLeftInternal() = v;
     }