[Fuchsia] Fix WebEngine to handle drop-down menus

Previously WebEngine was crashing when user clicks on a drop-down box.
The issue was that WindowParentingClient interface wasn't implemented
for root Aura windows that are used to host web frames. This CL adds
WindowParentingClient implementation. Also updated LayoutManager
implementation to handle drop-down menu windows properly.

Bug: fuchsia:34997, fuchsia:36350
Change-Id: I173febd62825dbe460844742451cc8581e41b3b9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1861039
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Auto-Submit: Sergey Ulanov <sergeyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#706265}

fuchsia/engine/browser/frame_impl.cc

@@ -30,6 +30,7 @@
 #include "mojo/public/cpp/system/platform_handle.h"
 #include "third_party/blink/public/common/associated_interfaces/associated_interface_provider.h"
 #include "third_party/blink/public/common/logging/logging_utils.h"
+#include "ui/aura/client/window_parenting_client.h"
 #include "ui/aura/layout_manager.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_tree_host_platform.h"
@@ -52,40 +53,56 @@ class PopupFrameCreationInfoUserData : public base::SupportsUserData::Data {
   fuchsia::web::PopupFrameCreationInfo info;
 };
 
-// Layout manager that allows only one child window and stretches it to fill the
-// parent.
+// Layout manager used for the root window that hosts the WebContents window.
+// The main WebContents window is stretched to occupy the whole parent. Note
+// that the root window may host other windows (particularly menus for drop-down
+// boxes). These windows get the location and size they request. The main
+// window for the web content is identified by window.type() ==
+// WINDOW_TYPE_CONTROL (set in WebContentsViewAura).
 class LayoutManagerImpl : public aura::LayoutManager {
  public:
   LayoutManagerImpl() = default;
   ~LayoutManagerImpl() override = default;
 
   // aura::LayoutManager implementation.
   void OnWindowResized() override {
-    // Resize the child to match the size of the parent
-    if (child_) {
-      SetChildBoundsDirect(child_,
-                           gfx::Rect(child_->parent()->bounds().size()));
+    // Resize the child to match the size of the parent.
+    if (main_child_) {
+      SetChildBoundsDirect(main_child_,
+                           gfx::Rect(main_child_->parent()->bounds().size()));
     }
   }
+
   void OnWindowAddedToLayout(aura::Window* child) override {
-    DCHECK(!child_);
-    child_ = child;
-    SetChildBoundsDirect(child_, gfx::Rect(child_->parent()->bounds().size()));
+    if (child->type() == aura::client::WINDOW_TYPE_CONTROL) {
+      DCHECK(!main_child_);
+      main_child_ = child;
+      SetChildBoundsDirect(main_child_,
+                           gfx::Rect(main_child_->parent()->bounds().size()));
+    }
   }
 
   void OnWillRemoveWindowFromLayout(aura::Window* child) override {
-    DCHECK_EQ(child, child_);
-    child_ = nullptr;
+    if (child->type() == aura::client::WINDOW_TYPE_CONTROL) {
+      DCHECK_EQ(child, main_child_);
+      main_child_ = nullptr;
+    }
   }
 
   void OnWindowRemovedFromLayout(aura::Window* child) override {}
+
   void OnChildWindowVisibilityChanged(aura::Window* child,
                                       bool visible) override {}
+
   void SetChildBounds(aura::Window* child,
-                      const gfx::Rect& requested_bounds) override {}
+                      const gfx::Rect& requested_bounds) override {
+    if (child != main_child_)
+      SetChildBoundsDirect(child, requested_bounds);
+  }
 
  private:
-  aura::Window* child_ = nullptr;
+  // The main window used for the WebContents.
+  aura::Window* main_child_ = nullptr;
 
   DISALLOW_COPY_AND_ASSIGN(LayoutManagerImpl);
 };
@@ -134,12 +151,36 @@ bool IsOriginWhitelisted(const GURL& url,
   return false;
 }
 
-class ScenicWindowTreeHost : public aura::WindowTreeHostPlatform {
+class WindowParentingClientImpl : public aura::client::WindowParentingClient {
  public:
-  explicit ScenicWindowTreeHost(ui::PlatformWindowInitProperties properties)
-      : aura::WindowTreeHostPlatform(std::move(properties)) {}
+  explicit WindowParentingClientImpl(aura::Window* root_window)
+      : root_window_(root_window) {
+    aura::client::SetWindowParentingClient(root_window_, this);
+  }
+  ~WindowParentingClientImpl() override {
+    aura::client::SetWindowParentingClient(root_window_, nullptr);
+  }
 
-  ~ScenicWindowTreeHost() override = default;
+  // WindowParentingClient implementation.
+  aura::Window* GetDefaultParent(aura::Window* window,
+                                 const gfx::Rect& bounds) override {
+    return root_window_;
+  }
+
+ private:
+  aura::Window* root_window_;
+
+  DISALLOW_COPY_AND_ASSIGN(WindowParentingClientImpl);
+};
+
+// WindowTreeHost that hosts web frames.
+class FrameWindowTreeHost : public aura::WindowTreeHostPlatform {
+ public:
+  explicit FrameWindowTreeHost(ui::PlatformWindowInitProperties properties)
+      : aura::WindowTreeHostPlatform(std::move(properties)),
+        window_parenting_client_(window()) {}
+
+  ~FrameWindowTreeHost() override = default;
 
   // Route focus & blur events to the window's focus observer and its
   // InputMethod.
@@ -154,7 +195,9 @@ class ScenicWindowTreeHost : public aura::WindowTreeHostPlatform {
   }
 
  private:
-  DISALLOW_COPY_AND_ASSIGN(ScenicWindowTreeHost);
+  WindowParentingClientImpl window_parenting_client_;
+
+  DISALLOW_COPY_AND_ASSIGN(FrameWindowTreeHost);
 };
 
 logging::LogSeverity ConsoleLogLevelToLoggingSeverity(
@@ -423,7 +466,7 @@ void FrameImpl::CreateView(fuchsia::ui::views::ViewToken view_token) {
   properties.view_ref_pair = scenic::ViewRefPair::New();
 
   window_tree_host_ =
-      std::make_unique<ScenicWindowTreeHost>(std::move(properties));
+      std::make_unique<FrameWindowTreeHost>(std::move(properties));
   window_tree_host_->InitHost();
 
   window_tree_host_->window()->GetHost()->AddEventRewriter(