Fix visual viewport for OOPIF.

content/browser/frame_host/render_widget_host_view_child_frame.cc

Index: content/browser/frame_host/render_widget_host_view_child_frame.cc
diff --git a/content/browser/frame_host/render_widget_host_view_child_frame.cc b/content/browser/frame_host/render_widget_host_view_child_frame.cc
index 7232c547aa112d80c6d0b0c8c2b2509cd0bda623..efaf5d366c20260e4396e58849a5816093ea986e 100644
--- a/content/browser/frame_host/render_widget_host_view_child_frame.cc
+++ b/content/browser/frame_host/render_widget_host_view_child_frame.cc
@@ -121,6 +121,28 @@ gfx::Rect RenderWidgetHostViewChildFrame::GetViewBounds() const {
   return rect;
 }
 
+gfx::Size RenderWidgetHostViewChildFrame::GetVisibleViewportSize() const {
+  // For subframes, the visual viewport corresponds to the main frame size, so
+  // this bubbles up to the parent until it will hit the main frame's
+  // RenderWidgetHostView.
+  //
+  // Currently this excludes webview guests, since they expect the visual
+  // viewport to return the guest's size rather than the page's; one reason why
+  // is that Blink ends up using the visual viewport to calculate things like
+  // window.innerWidth/innerHeight for main frames, and a guest is considered
+  // to be a main frame.  This should be cleaned up eventually.

[alexmos, 2016/03/26 00:00:48]

I'm not quite sure about this, and in general about what visual viewport means
for guests, so it'd be great to double-check this comment/logic.  I added the
|is_guest| exclusion because of tests like
WebViewTest.Shim_TestNavigateAfterResize/0.  With
--use-cross-process-frames-for-guests, this would return incorrect
window.innerWidth/Height for guest (embedder's size rather than guest's size)
without that exception.

For reference, here's the code from getViewportSize in LocalDOMWindow.cpp, which
is what's used for innerWidth/innerHeight:

    return frame->isMainFrame() && !host->settings().inertVisualViewport()
        ? FloatSize(host->visualViewport().visibleRect().size())
        : FloatSize(view->visibleContentRect(IncludeScrollbars).size());

For OOP subframes, we take the second path.  For a guest, we take the first
path.

[kenrb, 2016/03/31 17:41:58]

I don't quite understand what having a separate visual viewport for a guest
means, either. This seems reasonable to me, but do we expect to be able to
separately scale a guest from its embedder?

+  bool is_guest = BrowserPluginGuest::IsGuest(
+      static_cast<RenderViewHostImpl*>(RenderViewHost::From(host_)));
+  if (frame_connector_ && !is_guest) {
+    RenderWidgetHostView* parent_view =
+        frame_connector_->GetParentRenderWidgetHostView();
+    // The parent_view can be null in unit tests when using a TestWebContents.
+    if (parent_view)
+      return parent_view->GetVisibleViewportSize();
+  }
+  return GetViewBounds().size();
+}
+
 gfx::Vector2dF RenderWidgetHostViewChildFrame::GetLastScrollOffset() const {
   return last_scroll_offset_;
 }