diff -r 000000000000 -r 6474c204b198 layout/generic/nsPageContentFrame.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/generic/nsPageContentFrame.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,118 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+#include "nsPageContentFrame.h"
+#include "nsCSSFrameConstructor.h"
+#include "nsPresContext.h"
+#include "nsGkAtoms.h"
+#include "nsIPresShell.h"
+#include "nsSimplePageSequenceFrame.h"
+
+nsIFrame*
+NS_NewPageContentFrame(nsIPresShell* aPresShell, nsStyleContext* aContext)
+{
+  return new (aPresShell) nsPageContentFrame(aContext);
+}
+
+NS_IMPL_FRAMEARENA_HELPERS(nsPageContentFrame)
+
+nsresult
+nsPageContentFrame::Reflow(nsPresContext*           aPresContext,
+                           nsHTMLReflowMetrics&     aDesiredSize,
+                           const nsHTMLReflowState& aReflowState,
+                           nsReflowStatus&          aStatus)
+{
+  DO_GLOBAL_REFLOW_COUNT("nsPageContentFrame");
+  DISPLAY_REFLOW(aPresContext, this, aReflowState, aDesiredSize, aStatus);
+  aStatus = NS_FRAME_COMPLETE;  // initialize out parameter
+  nsresult rv = NS_OK;
+
+  if (GetPrevInFlow() && (GetStateBits() & NS_FRAME_FIRST_REFLOW)) {
+    nsresult rv = aPresContext->PresShell()->FrameConstructor()
+                    ->ReplicateFixedFrames(this);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  // Set our size up front, since some parts of reflow depend on it
+  // being already set.  Note that the computed height may be
+  // unconstrained; that's ok.  Consumers should watch out for that.
+  nsSize  maxSize(aReflowState.ComputedWidth(),
+                  aReflowState.ComputedHeight());
+  SetSize(maxSize);
+ 
+  // A PageContentFrame must always have one child: the canvas frame.
+  // Resize our frame allowing it only to be as big as we are
+  // XXX Pay attention to the page's border and padding...
+  if (mFrames.NotEmpty()) {
+    nsIFrame* frame = mFrames.FirstChild();
+    nsHTMLReflowState kidReflowState(aPresContext, aReflowState, frame, maxSize);
+    kidReflowState.SetComputedHeight(maxSize.height);
+
+    // Reflow the page content area
+    rv = ReflowChild(frame, aPresContext, aDesiredSize, kidReflowState, 0, 0, 0, aStatus);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    // The document element's background should cover the entire canvas, so
+    // take into account the combined area and any space taken up by
+    // absolutely positioned elements
+    nsMargin padding(0,0,0,0);
+
+    // XXXbz this screws up percentage padding (sets padding to zero
+    // in the percentage padding case)
+    kidReflowState.mStylePadding->GetPadding(padding);
+
+    // This is for shrink-to-fit, and therefore we want to use the
+    // scrollable overflow, since the purpose of shrink to fit is to
+    // make the content that ought to be reachable (represented by the
+    // scrollable overflow) fit in the page.
+    if (frame->HasOverflowAreas()) {
+      // The background covers the content area and padding area, so check
+      // for children sticking outside the child frame's padding edge
+      nscoord xmost = aDesiredSize.ScrollableOverflow().XMost();
+      if (xmost > aDesiredSize.Width()) {
+        nscoord widthToFit = xmost + padding.right +
+          kidReflowState.mStyleBorder->GetComputedBorderWidth(NS_SIDE_RIGHT);
+        float ratio = float(maxSize.width) / widthToFit;
+        NS_ASSERTION(ratio >= 0.0 && ratio < 1.0, "invalid shrink-to-fit ratio");
+        mPD->mShrinkToFitRatio = std::min(mPD->mShrinkToFitRatio, ratio);
+      }
+    }
+
+    // Place and size the child
+    FinishReflowChild(frame, aPresContext, aDesiredSize, &kidReflowState, 0, 0, 0);
+
+    NS_ASSERTION(aPresContext->IsDynamic() || !NS_FRAME_IS_FULLY_COMPLETE(aStatus) ||
+                  !frame->GetNextInFlow(), "bad child flow list");
+  }
+
+  // Reflow our fixed frames
+  nsReflowStatus fixedStatus = NS_FRAME_COMPLETE;
+  ReflowAbsoluteFrames(aPresContext, aDesiredSize, aReflowState, fixedStatus);
+  NS_ASSERTION(NS_FRAME_IS_COMPLETE(fixedStatus), "fixed frames can be truncated, but not incomplete");
+
+  // Return our desired size
+  aDesiredSize.Width() = aReflowState.ComputedWidth();
+  if (aReflowState.ComputedHeight() != NS_UNCONSTRAINEDSIZE) {
+    aDesiredSize.Height() = aReflowState.ComputedHeight();
+  }
+
+  FinishAndStoreOverflow(&aDesiredSize);
+
+  NS_FRAME_SET_TRUNCATION(aStatus, aReflowState, aDesiredSize);
+  return NS_OK;
+}
+
+nsIAtom*
+nsPageContentFrame::GetType() const
+{
+  return nsGkAtoms::pageContentFrame; 
+}
+
+#ifdef DEBUG_FRAME_DUMP
+nsresult
+nsPageContentFrame::GetFrameName(nsAString& aResult) const
+{
+  return MakeFrameName(NS_LITERAL_STRING("PageContent"), aResult);
+}
+#endif