[Slimming Paint] Move PageWidgetDelegate scale to a transform display item.

Source/web/PageWidgetDelegate.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 18 matching lines @@
  */
 
 #include "config.h"
 #include "web/PageWidgetDelegate.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/page/AutoscrollController.h"
 #include "core/page/EventHandler.h"
 #include "core/page/Page.h"
+#include "core/paint/TransformRecorder.h"
 #include "core/rendering/RenderView.h"
 #include "core/rendering/compositing/RenderLayerCompositor.h"
 #include "platform/Logging.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/paint/ClipRecorder.h"
 #include "platform/graphics/paint/DisplayItemList.h"
 #include "platform/graphics/paint/DrawingRecorder.h"
+#include "platform/transforms/AffineTransform.h"
 #include "public/web/WebInputEvent.h"
 #include "web/PageOverlayList.h"
 #include "web/WebInputEventConversion.h"
 #include "wtf/CurrentTime.h"
 
 namespace blink {
 
 void PageWidgetDelegate::animate(Page& page, double monotonicFrameBeginTime, LocalFrame& root)
 {
     RefPtrWillBeRawPtr<FrameView> view = root.view();
@@ skipping 19 matching lines @@
         displayItemList = DisplayItemList::create();
         graphicsContext = adoptPtr(new GraphicsContext(nullptr, displayItemList.get()));
     } else {
         graphicsContext = adoptPtr(new GraphicsContext(canvas, nullptr));
     }
 
     // FIXME: opaqueness and device scale factor settings are layering violations and should not
     // be used within Blink paint code.
     graphicsContext->setCertainlyOpaque(background == Opaque);
     float scaleFactor = page.deviceScaleFactor();
-    graphicsContext->scale(scaleFactor, scaleFactor);
     graphicsContext->setDeviceScaleFactor(scaleFactor);
+
+    AffineTransform scale;
+    scale.scale(scaleFactor);
+    TransformRecorder scaleRecorder(*graphicsContext, root.displayItemClient(), scale);

[jbroman, 2015/01/27 22:02:28]

Is it fine to use the LocalFrame for this display item? I think so, and I think
invalidation is probably fine for the same reason other uses of it here are
(because the LocalFrame outlives its GraphicsLayers?).

TransformRecorder has a hardcoded DisplayItem::Type, but I can't find anywhere
else it would conflict with. Is this fine, or is there some policy describing
what DisplayItem::Type should be used here? 

[chrishtr, 2015/01/28 01:50:21]

It's fine. The only requirement is that the (DisplayItemClient,
DisplayItem::Type) pair be unique. But for readability the type should be chosen
to make sense, and not be one of the DrawwPaintPase* enum values unless it's
actually the drawing item for that phase of the official web painting algorithm.

(There are other cases where we actually, and incorrectly, violate that, in
particular cases with multiple types of clip on the same object.

+
     IntRect dirtyRect(rect);
     FrameView* view = root.view();
     if (view) {
         ClipRecorder clipRecorder(root.displayItemClient(), graphicsContext.get(), DisplayItem::PageWidgetDelegateClip, dirtyRect);
 
         view->paint(graphicsContext.get(), dirtyRect);
         if (overlays)
             overlays->paintWebFrame(*graphicsContext);
     } else {
         DrawingRecorder drawingRecorder(graphicsContext.get(), root.displayItemClient(), DisplayItem::PageWidgetDelegateBackgroundFallback, dirtyRect);
@@ skipping 112 matching lines @@
 {
     return mainFrame.eventHandler().handleWheelEvent(PlatformWheelEventBuilder(mainFrame.view(), event));
 }
 
 bool PageWidgetEventHandler::handleTouchEvent(LocalFrame& mainFrame, const WebTouchEvent& event)
 {
     return mainFrame.eventHandler().handleTouchEvent(PlatformTouchEventBuilder(mainFrame.view(), event));
 }
 
 } // namespace blink