diff -r 000000000000 -r 6474c204b198 layout/generic/nsFontInflationData.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/generic/nsFontInflationData.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,75 @@
+/* vim: set shiftwidth=2 tabstop=8 autoindent cindent expandtab: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* Per-block-formatting-context manager of font size inflation for pan and zoom UI. */
+
+#ifndef nsFontInflationData_h_
+#define nsFontInflationData_h_
+
+#include "nsIFrame.h"
+
+struct nsHTMLReflowState;
+
+class nsFontInflationData
+{
+public:
+
+  static nsFontInflationData* FindFontInflationDataFor(const nsIFrame *aFrame);
+
+  // Returns whether the effective width changed (which requires the
+  // caller to mark its descendants dirty
+  static bool
+    UpdateFontInflationDataWidthFor(const nsHTMLReflowState& aReflowState);
+
+  static void MarkFontInflationDataTextDirty(nsIFrame *aFrame);
+
+  bool InflationEnabled() {
+    if (mTextDirty) {
+      ScanText();
+    }
+    return mInflationEnabled;
+  }
+
+  nscoord EffectiveWidth() const {
+    return mNCAWidth;
+  }
+
+private:
+
+  nsFontInflationData(nsIFrame* aBFCFrame);
+
+  nsFontInflationData(const nsFontInflationData&) MOZ_DELETE;
+  void operator=(const nsFontInflationData&) MOZ_DELETE;
+
+  void UpdateWidth(const nsHTMLReflowState &aReflowState);
+  enum SearchDirection { eFromStart, eFromEnd };
+  static nsIFrame* FindEdgeInflatableFrameIn(nsIFrame *aFrame,
+                                             SearchDirection aDirection);
+
+  void MarkTextDirty() { mTextDirty = true; }
+  void ScanText();
+  // Scan text in the subtree rooted at aFrame.  Increment mTextAmount
+  // by multiplying the number of characters found by the font size
+  // (yielding the width that would be occupied by the characters if
+  // they were all em squares).  But stop scanning if mTextAmount
+  // crosses mTextThreshold.
+  void ScanTextIn(nsIFrame *aFrame);
+
+  static const nsIFrame* FlowRootFor(const nsIFrame *aFrame)
+  {
+    while (!(aFrame->GetStateBits() & NS_FRAME_FONT_INFLATION_FLOW_ROOT)) {
+      aFrame = aFrame->GetParent();
+    }
+    return aFrame;
+  }
+
+  nsIFrame *mBFCFrame;
+  nscoord mNCAWidth;
+  nscoord mTextAmount, mTextThreshold;
+  bool mInflationEnabled; // for this BFC
+  bool mTextDirty;
+};
+
+#endif /* !defined(nsFontInflationData_h_) */