blink::Page: Move main_frame declaration

Page::main_frame_ is used during constructing Page::visual_viewport_
(VisualViewport) which imples that the field should be constructed
before using.

allocatd memory.

Note: In practice this works because Oilpan currently 0-fills all newly
Change-Id: I103d90c17d649dffbce2c9ac70a0a6a9cac9448b
Reviewed-on: https://chromium-review.googlesource.com/1133159Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574139}

third_party/blink/renderer/core/page/page.cc

@@ -145,6 +145,7 @@ Page* Page::CreateOrdinary(PageClients& page_clients, Page* opener) {
 
 Page::Page(PageClients& page_clients)
     : SettingsDelegate(Settings::Create()),
+      main_frame_(nullptr),
       animator_(PageAnimator::Create(*this)),
       autoscroll_controller_(AutoscrollController::Create(*this)),
       chrome_client_(page_clients.chrome_client),
@@ -161,7 +162,6 @@ Page::Page(PageClients& page_clients)
       visual_viewport_(VisualViewport::Create(*this)),
       overscroll_controller_(
           OverscrollController::Create(GetVisualViewport(), GetChromeClient())),
-      main_frame_(nullptr),
       plugin_data_(nullptr),
       opened_by_dom_(false),
       tab_key_cycles_through_elements_(true),

third_party/blink/renderer/core/page/page.h

@@ -332,6 +332,20 @@ class CORE_EXPORT Page final : public GarbageCollectedFinalized<Page>,
 
   void SetPageScheduler(std::unique_ptr<PageScheduler>);
 
+  // Typically, the main frame and Page should both be owned by the embedder,
+  // which must call Page::willBeDestroyed() prior to destroying Page. This
+  // call detaches the main frame and clears this pointer, thus ensuring that
+  // this field only references a live main frame.
+  //
+  // However, there are several locations (InspectorOverlay, SVGImage, and
+  // WebPagePopupImpl) which don't hold a reference to the main frame at all
+  // after creating it. These are still safe because they always create a
+  // Frame with a LocalFrameView. LocalFrameView and Frame hold references to
+  // each other, thus keeping each other alive. The call to willBeDestroyed()
+  // breaks this cycle, so the frame is still properly destroyed once no
+  // longer needed.
+  Member<Frame> main_frame_;
+
   Member<PageAnimator> animator_;
   const Member<AutoscrollController> autoscroll_controller_;
   Member<ChromeClient> chrome_client_;
@@ -350,20 +364,6 @@ class CORE_EXPORT Page final : public GarbageCollectedFinalized<Page>,
   const Member<VisualViewport> visual_viewport_;
   const Member<OverscrollController> overscroll_controller_;
 
-  // Typically, the main frame and Page should both be owned by the embedder,
-  // which must call Page::willBeDestroyed() prior to destroying Page. This
-  // call detaches the main frame and clears this pointer, thus ensuring that
-  // this field only references a live main frame.
-  //
-  // However, there are several locations (InspectorOverlay, SVGImage, and
-  // WebPagePopupImpl) which don't hold a reference to the main frame at all
-  // after creating it. These are still safe because they always create a
-  // Frame with a LocalFrameView. LocalFrameView and Frame hold references to
-  // each other, thus keeping each other alive. The call to willBeDestroyed()
-  // breaks this cycle, so the frame is still properly destroyed once no
-  // longer needed.
-  Member<Frame> main_frame_;
-
   Member<PluginData> plugin_data_;
 
   Member<ValidationMessageClient> validation_message_client_;