Ensure VisualViewport reset when local mainframe is converted to remote.

This CL ensures that when a local mainframe is converted to a remote one
that the VisualViewport for the new mainframe is reset. This is
important since non-unit PageScaleFactor should only be stored for
local mainframes, otherwise the scale will be innappropriately removed
from event coordinates in out-of-process iframes.

Bug: 1150977
Change-Id: I4dc8cc4ea0c4521a2f999c97607671ff62d4d159
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2629491
Commit-Queue: James MacLean <wjmaclean@chromium.org>
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844148}

third_party/blink/renderer/core/frame/visual_viewport.cc

@@ -499,8 +499,15 @@ double VisualViewport::VisibleHeightCSSPx() const {
 bool VisualViewport::DidSetScaleOrLocation(float scale,
                                            bool is_pinch_gesture_active,
                                            const FloatPoint& location) {
-  if (!LocalMainFrame())
+  if (!LocalMainFrame()) {
+    is_pinch_gesture_active_ = is_pinch_gesture_active;
+    // The VisualViewport for a remote mainframe must always be 1.0 or else
+    // event targeting will fail.
+    DCHECK(scale == 1.f);
+    scale_ = scale;
+    offset_ = ScrollOffset();
     return false;
+  }
 
   bool values_changed = false;
 

third_party/blink/renderer/core/frame/web_frame_test.cc

@@ -8843,6 +8843,19 @@ TEST_F(WebFrameSwapTest, SwapMainFrame) {
   EXPECT_EQ("hello", content);
 }
 
+TEST_F(WebFrameSwapTest, SwapMainFrameWithPageScaleReset) {
+  WebView()->SetDefaultPageScaleLimits(1, 2);
+  WebView()->SetPageScaleFactor(1.25);
+  EXPECT_EQ(1.25, WebView()->PageScaleFactor());
+
+  WebRemoteFrame* remote_frame = frame_test_helpers::CreateRemote();
+  MainFrame()->Swap(remote_frame);
+  EXPECT_EQ(1.0, WebView()->PageScaleFactor());
+  // Note: if we were to extend this test to call frame_test_helpers::LoadFrame
+  // as in WebFrameSwapTest.SwapMainFrame, then an appropriate binding must be
+  // provided for the AssociatedRemote.
+}
+
 TEST_F(WebFrameSwapTest, ValidateSizeOnRemoteToLocalMainFrameSwap) {
   gfx::Size size(111, 222);
 

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

@@ -333,6 +333,7 @@ void Page::SetMainFrame(Frame* main_frame) {
   main_frame_ = main_frame;
 
   page_scheduler_->SetIsMainFrameLocal(main_frame->IsLocalFrame());
+  visual_viewport_->Reset();
 }
 
 LocalFrame* Page::DeprecatedLocalMainFrame() const {