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

Source/web/PageWidgetDelegate.cpp

Index: Source/web/PageWidgetDelegate.cpp
diff --git a/Source/web/PageWidgetDelegate.cpp b/Source/web/PageWidgetDelegate.cpp
index 9f53c7e49e0d79ac297cfc17cd82f181b4b05bf2..79d403b666db2672ae50ba2d7ef7a7b1a49b38b3 100644
--- a/Source/web/PageWidgetDelegate.cpp
+++ b/Source/web/PageWidgetDelegate.cpp
@@ -36,6 +36,7 @@
 #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"
@@ -43,6 +44,7 @@
 #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"
@@ -82,8 +84,12 @@ void PageWidgetDelegate::paint(Page& page, PageOverlayList* overlays, WebCanvas*
     // 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) {