Avoid division-by-zero when visual viewport width is 0.

third_party/WebKit/Source/core/frame/FrameView.cpp

Index: third_party/WebKit/Source/core/frame/FrameView.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameView.cpp b/third_party/WebKit/Source/core/frame/FrameView.cpp
index fc8f37723622c32a6de17ab60b65e731e45b1271..21257bd9015ef7bcaa7b7126d3c7314f91ccb3ce 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -1353,7 +1353,8 @@ FloatSize FrameView::viewportSizeForViewportUnits() const {
   // height, compensating for page scale as well, since we want to use the
   // viewport with browser controls hidden for vh (to match Safari).
   BrowserControls& browserControls = m_frame->host()->browserControls();
-  if (m_frame->isMainFrame() && size.width()) {
+  if (m_frame->isMainFrame() && size.width() &&
+      m_frame->host()->visualViewport().size().width()) {

[rune, 2016/12/09 15:27:50]

I should probably check the pageScaleAtLayoutWidth for 0 below instead ...

[bokan, 2016/12/09 16:48:55]

Visual Viewport size should never be 0, do you know why that happens? Sigh...I
battled many size regressions related to extensions and their autosizing
behavior but I thought it was over...

     float pageScaleAtLayoutWidth =
         m_frame->host()->visualViewport().size().width() / size.width();
     size.expand(0, browserControls.height() / pageScaleAtLayoutWidth);