Bug 1209697: Cache flex measuring reflows to avoid exponential behavior

layout/generic/nsFlexContainerFrame.h

@@ -56,6 +56,7 @@ public:
   class FlexLine;
   class FlexboxAxisTracker;
   struct StrutInfo;
+  struct CachedMeasuringReflowResult;
 
   // nsIFrame overrides
   void Init(nsIContent*       aContent,
@@ -66,6 +67,8 @@ public:
                                 const nsRect&           aDirtyRect,
                                 const nsDisplayListSet& aLists) override;
 
+  void MarkIntrinsicISizesDirty() override;
+
   virtual void Reflow(nsPresContext*           aPresContext,
                       ReflowOutput&     aDesiredSize,
                       const ReflowInput& aReflowInput,
@@ -194,6 +197,18 @@ protected:
                                      const ReflowInput& aParentReflowInput,
                                      const FlexboxAxisTracker& aAxisTracker);
 
+  /**
+   * This method gets a cached measuring reflow for a flex item, or does it and
+   * caches it.
+   *
+   * This avoids exponential reflows, see the comment on
+   * CachedMeasuringReflowResult.
+   */
+  const CachedMeasuringReflowResult& MeasureAscentAndHeightForFlexItem(
+    FlexItem& aItem,
+    nsPresContext* aPresContext,
+    ReflowInput& aChildReflowInput);
+
   /**
    * This method performs a "measuring" reflow to get the content height of
    * aFlexItem.Frame() (treating it as if it had auto-height), & returns the