Fix webview crash on attempt to scroll.

content/browser/frame_host/render_widget_host_view_guest.cc

Index: content/browser/frame_host/render_widget_host_view_guest.cc
diff --git a/content/browser/frame_host/render_widget_host_view_guest.cc b/content/browser/frame_host/render_widget_host_view_guest.cc
index 54d6c4c3875d8c0eabd4aa24dbb0081fad74c5fa..534ffa02e79f1583ff680b290cfc5dcae88c72da 100644
--- a/content/browser/frame_host/render_widget_host_view_guest.cc
+++ b/content/browser/frame_host/render_widget_host_view_guest.cc
@@ -74,6 +74,7 @@ RenderWidgetHostViewGuest::RenderWidgetHostViewGuest(
       // |guest| is NULL during test.
       guest_(guest ? guest->AsWeakPtr() : base::WeakPtr<BrowserPluginGuest>()),
       platform_view_(platform_view) {
+  UpdateScreenInfo(GetNativeView());

[khmel, 2016/05/27 20:49:26]

Direct reason of crash current_device_scale_factor_ = 0 (default value) from
RenderWidgetHostViewBase. This field is updated on UpdateScreenInfo. When we
handle gesture events, we temporary set scale device factor 1.0 and restore then
to current_device_scale_factor_ value, which is 0. That is why scroll does not
work.

Update scale factor is here:
https://code.google.com/p/chromium/codesearch#chromium/src/content/browser/fr...

[wjmaclean, 2016/05/30 14:00:51]

This looks fine, though I recall noting recently that we also don't properly set
current_device_scale_factor_ for OOPIF WebView, i.e. when we use
RenderWidgetHostViewChildFrame. Can this call be made instead in RWHVCF's
constructor? If it can, that would prevent this problem from recurring when we
transition to using just RWHVCF.

I believe RWHVCF also has a unit test file somewhere, so we should add test
coverage for this as well.

[khmel, 2016/06/02 00:10:22]

It is hard to put it to RWHVCF CTOR because RWHVCF has method 
gfx::NativeView RenderWidgetHostViewChildFrame::GetNativeView() const {
  NOTREACHED();
  return nullptr;
}

Calling it from its CTORS goes to crash.

I extended browser_tests to validate this. Without this fix new test fails.

[wjmaclean, 2016/06/02 12:17:52]

We're going to be removing the NOTREACHED() in RWHVCF::GetNativeView() soon, so
perhaps we'll move this when that happens.

 }
 
 RenderWidgetHostViewGuest::~RenderWidgetHostViewGuest() {}