Don't invalidate width for children unless scrollbars have changed.

third_party/WebKit/LayoutTests/css3/flexbox/scrollbars-changed-expected.txt

Index: third_party/WebKit/LayoutTests/css3/flexbox/scrollbars-changed-expected.txt
diff --git a/third_party/WebKit/LayoutTests/fast/repaint/reflection-repaint-test-expected.txt b/third_party/WebKit/LayoutTests/css3/flexbox/scrollbars-changed-expected.txt
similarity index 63%
copy from third_party/WebKit/LayoutTests/fast/repaint/reflection-repaint-test-expected.txt
copy to third_party/WebKit/LayoutTests/css3/flexbox/scrollbars-changed-expected.txt
index 2786e996b38d6b20d4f28078ee304e269905ce35..68157a45155ff568872a7f3e4777f730f5184bd8 100644
--- a/third_party/WebKit/LayoutTests/fast/repaint/reflection-repaint-test-expected.txt
+++ b/third_party/WebKit/LayoutTests/css3/flexbox/scrollbars-changed-expected.txt
@@ -9,18 +9,18 @@
       "drawsContent": true,
       "paintInvalidations": [
         {
-          "object": "LayoutBlockFlow DIV id='target'",
-          "rect": [22, 50, 226, 166],
+          "object": "LayoutBlockFlow DIV id='dynamic' class='content'",
+          "rect": [0, 0, 185, 20],
           "reason": "invalidate paint rectangle"
         },
         {
-          "object": "LayoutBlockFlow DIV id='target'",
-          "rect": [22, 50, 226, 166],
-          "reason": "invalidate paint rectangle"
+          "object": "LayoutBlockFlow DIV id='scroller'",
+          "rect": [185, 0, 15, 100],
+          "reason": "scroll"
         },
         {
           "object": "LayoutText #text",
-          "rect": [23, 51, 71, 109],
+          "rect": [0, 5, 15, 15],
           "reason": "full"
         }
       ]
@@ -36,11 +36,11 @@
       "reason": "full"
     },
     {
-      "object": "LayoutBlockFlow DIV id='target'",
-      "reason": "invalidate paint rectangle"
+      "object": "VerticalScrollbar",
+      "reason": "scroll"
     },
     {
-      "object": "LayoutBlockFlow DIV id='target'",
+      "object": "LayoutBlockFlow DIV id='dynamic' class='content'",
       "reason": "invalidate paint rectangle"
     },
     {
@@ -48,7 +48,7 @@
       "reason": "full"
     },
     {
-      "object": "InlineTextBox 'PASS'",
+      "object": "InlineTextBox 'z'",
       "reason": "full"
     }
   ]