Implement desktop compatibility viewport

cc/layer_tree_host.cc

Index: cc/layer_tree_host.cc
diff --git a/cc/layer_tree_host.cc b/cc/layer_tree_host.cc
index 9386699d42d4b2aa84fb560332e621d5c45565aa..e7375566129356531e581ba8385835b79195bd0f 100644
--- a/cc/layer_tree_host.cc
+++ b/cc/layer_tree_host.cc
@@ -311,6 +311,14 @@ void LayerTreeHost::finishCommitOnImplThread(LayerTreeHostImpl* hostImpl)
     hostImpl->setDebugState(m_debugState);
     hostImpl->savePaintTime(m_renderingStats.totalPaintTime);
 
+    if (LayerImpl* rootScrollLayer = syncTree->RootScrollLayer()) {
+        fprintf (stderr, "debug: %d %d\n", rootScrollLayer->sentDesktopCompatibilityViewportOffsetFromScrollPositionDelta().x(), rootScrollLayer->sentDesktopCompatibilityViewportOffsetFromScrollPositionDelta().y());
+        // FIXME FIXME FIXME
+        rootScrollLayer->setDesktopCompatibilityViewportOffsetFromScrollPosition(rootScrollLayer->desktopCompatibilityViewportOffsetFromScrollPosition() + rootScrollLayer->sentDesktopCompatibilityViewportOffsetFromScrollPositionDelta());
+        rootScrollLayer->setDesktopCompatibilityViewportOffsetFromScrollPositionDelta(rootScrollLayer->desktopCompatibilityViewportOffsetFromScrollPositionDelta() - rootScrollLayer->sentDesktopCompatibilityViewportOffsetFromScrollPositionDelta());
+        rootScrollLayer->setSentDesktopCompatibilityViewportOffsetFromScrollPositionDelta(gfx::Vector2d());
+    }
+
     if (newImplTreeHasNoEvictedResources) {
         if (syncTree->ContentsTexturesPurged())
             syncTree->ResetContentsTexturesPurged();
@@ -748,8 +756,8 @@ void LayerTreeHost::applyScrollAndScale(const ScrollAndScaleSet& info)
         else
             layer->setScrollOffset(layer->scrollOffset() + info.scrolls[i].scrollDelta);
     }
-    if (!rootScrollDelta.IsZero() || info.pageScaleDelta != 1)
-        m_client->applyScrollAndScale(rootScrollDelta, info.pageScaleDelta);
+    if (!rootScrollDelta.IsZero() || info.pageScaleDelta != 1 || !info.desktopCompatibilityViewportOffsetFromScrollPositionDelta.IsZero())
+        m_client->applyScrollAndScale(rootScrollDelta, info.pageScaleDelta, info.desktopCompatibilityViewportOffsetFromScrollPositionDelta);
 }
 
 void LayerTreeHost::setImplTransform(const gfx::Transform& transform)