[css-flexbox] Reimplement min-width: auto

Specified in http://dev.w3.org/csswg/css-flexbox/#min-size-auto

We previously had this implemented, but reverted it in:
https://bugs.webkit.org/show_bug.cgi?id=111790

The spec has since re-added it with some tweaks. This patch
implements the new behavior and updates related tests and
devtools UI to match.

In case this patch breaks any website or chrome UI, the fix
is likely to add:

  min-width: 0;
  min-height: 0;

to any relevant flexitems.

flexbox-flex-direction-column.html is a CSSWG test that also covers min-width.
    
Once we import the official tests, we should remove our local copies.

BUG=426898

Review URL: https://codereview.chromium.org/988523003

git-svn-id: svn://svn.chromium.org/blink/trunk@193665 bbb929c8-8fbe-4397-9dbb-9b2b20218538
diff --git a/Source/core/css/html.css b/Source/core/css/html.css
index 8253c91..9588b1d 100644
--- a/Source/core/css/html.css
+++ b/Source/core/css/html.css
@@ -610,6 +610,7 @@
 
 input[type="range" i]::-webkit-slider-container, input[type="range" i]::-webkit-media-slider-container {
     flex: 1;
+    min-width: 0;
     box-sizing: border-box;
     -webkit-user-modify: read-only !important;
     display: flex;
@@ -617,6 +618,7 @@
 
 input[type="range" i]::-webkit-slider-runnable-track {
     flex: 1;
+    min-width: 0;
     -webkit-align-self: center;
 
     box-sizing: border-box;
@@ -697,6 +699,7 @@
     background-color: #000000;
     border: 1px solid #777777;
     flex: 1;
+    min-width: 0;
     -webkit-user-modify: read-only !important;
 }