Bug 1500608: Don't skip the flex-item early-freeze for devtools after…

… all. r=bradwerth

This patch basically reverts the functional part of changeset 52bd865d757c.
I'd optimistically hoped we could skip this early-freeze in order to compute &
report a bit more "potential flexing" information via devtools.  Bbut it turns
out that breaks assertions & produces bogus information for flex items whose
base size vs. min/max-clamped "hypothetical" sizes are very
different. (Specifically: it produces nonsense for flex items whose base sizes,
if unclamped, would reverse the directionality of flexing.)

Differential Revision: https://phabricator.services.mozilla.com/D9304

--HG--
extra : moz-landing-system : lando

dom/flex/test/chrome/test_flex_items.html

@@ -15,6 +15,13 @@
     /* This just needs to be large enough so that no shrinking is required. */
     width: 1600px;
   }
+  .clamped-huge-item {
+    flex: 1 1 1650px; /* This needs to be bigger than #flex-sanity, to test
+                         the scenario it's aiming to test (early clamping of a
+                         flex item which, if left unclamped, would've reversed
+                         the direction of flexing & made everything shrink). */
+    max-width: 10px;
+  }
 
   .base        { align-self: baseline; }
   .lastbase    { align-self: last baseline; }
@@ -144,6 +151,9 @@
       mainDeltaSize: 0 },
     { mainBaseSize: 50,
       mainMaxSize: 10 },
+    { mainBaseSize: 1650,
+      mainMaxSize: 10,
+      mainDeltaSize: 0 },
     { mainDeltaSize: 0 },
     { /* final item is anonymous flex item */ },
   ];
@@ -241,6 +251,7 @@
     <!-- Item that wants to grow but is trivially clamped to max-width
          below base size: -->
     <div style="flex: 1 1 50px; max-width: 10px"></div>
+    <div class="clamped-huge-item"></div>
     <div style="display:contents">
       <div class="white">replaced</div>
     </div>

layout/generic/nsFlexContainerFrame.cpp

@@ -2534,13 +2534,7 @@ FlexLine::FreezeItemsEarly(bool aIsUsingFlexGrow,
     if (!item->IsFrozen()) {
       numUnfrozenItemsToBeSeen--;
       bool shouldFreeze = (0.0f == item->GetFlexFactor(aIsUsingFlexGrow));
-      // NOTE: We skip the "could flex but base size out of range"
-      // early-freezing if flex devtools are active, so that we can let the
-      // first run of the main flex layout loop compute how much this item
-      // wants to flex. (This skipping shouldn't impact results, because
-      // any affected items will just immediately be caught & frozen as min/max
-      // violations in that first loop, and that'll trigger another loop.)
-      if (!shouldFreeze && !aLineInfo) {
+      if (!shouldFreeze) {
         if (aIsUsingFlexGrow) {
           if (item->GetFlexBaseSize() > item->GetMainSize()) {
             shouldFreeze = true;