Bug 1022825 - Implement Asynchronous Smooth Scrolling on Compositor Thread. r=kats

- Extended nsIScrollableFrame and nsGfxScrollFrame to return destination
  of smooth scrolls which are to be animated on the compositor thread.
- Added apz.smooth_scroll_repaint_interval preference.
- Implemented AsyncPanZoomController::PanZoomState::SMOOTH_MSD_SCROLL state
  and AsyncPanZoomController::SmoothScrollAnimation class to animate smooth
  scroll animations on the compositor thread.
- Extended FrameMetrics to report requests for smooth scrolls to be animated
  on the compositor thread and their corresponding destination positions.
- AsyncPanZoomController now checks FrameMetrics for requests to perform
  smooth scrolling on the compositor thread.  It will ensure that they
  are cancelled as needed by mousewheel, touchpanel, keyboard, and
  CSSOM-View instant scrolling DOM methods.
- The layout/generic/test/test_scroll_behavior.html mochitest has been
  commented as depending on Bug 1062609 before being enabled for APZ.

gfx/layers/LayersLogging.cpp

@@ -121,6 +121,9 @@ AppendToString(std::stringstream& aStream, const FrameMetrics& m,
   AppendToString(aStream, m.mCompositionBounds, "{ cb=");
   AppendToString(aStream, m.mScrollableRect, " sr=");
   AppendToString(aStream, m.GetScrollOffset(), " s=");
+  if (m.GetDoSmoothScroll()) {
+    AppendToString(aStream, m.GetSmoothScrollOffset(), " ss=");
+  }
   AppendToString(aStream, m.mDisplayPort, " dp=");
   AppendToString(aStream, m.mCriticalDisplayPort, " cdp=");
   AppendToString(aStream, m.GetBackgroundColor(), " color=");
@@ -139,8 +142,9 @@ AppendToString(std::stringstream& aStream, const FrameMetrics& m,
             m.mDevPixelsPerCSSPixel.scale, m.mResolution.scale,
             m.mCumulativeResolution.scale, m.GetZoom().scale,
             m.mTransformScale.scale).get();
-    aStream << nsPrintfCString(" u=(%d %lu)",
-            m.GetScrollOffsetUpdated(), m.GetScrollGeneration()).get();
+    aStream << nsPrintfCString(" u=(%d %d %lu)",
+            m.GetScrollOffsetUpdated(), m.GetDoSmoothScroll(),
+            m.GetScrollGeneration()).get();
     AppendToString(aStream, m.GetScrollParentId(), " p=");
     aStream << nsPrintfCString(" i=(%ld %lld) }",
             m.GetPresShellId(), m.GetScrollId()).get();