Cross-origin iframes: collect data under hypothetical loading strategies

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 92b46e9a1c3850ba0c0b3fbf8bcaefc9d77e9724..58829902ff0815adc4c0e090f00d2e436e22cb75 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -125,6 +125,7 @@
 #include "wtf/CurrentTime.h"
 #include "wtf/PtrUtil.h"
 #include "wtf/StdLibExtras.h"
+#include <algorithm>
 #include <memory>
 
 // Used to check for dirty layouts violating document lifecycle rules.
@@ -175,7 +176,6 @@ FrameView::FrameView(LocalFrame& frame)
       m_didScrollTimer(this, &FrameView::didScrollTimerFired),
       m_browserControlsViewportAdjustment(0),
       m_needsUpdateWidgetGeometries(false),
-      m_needsUpdateViewportIntersection(true),
 #if ENABLE(ASSERT)
       m_hasBeenDisposed(false),
 #endif
@@ -315,7 +315,7 @@ void FrameView::setupRenderThrottling() {
                          [](FrameView* frameView, bool isVisible) {
                            frameView->updateRenderThrottlingStatus(
                                !isVisible, frameView->m_subtreeThrottled);
-                           frameView->maybeRecordLoadReason();
+                           frameView->recordDeferredLoadingStats();
                          },
                          wrapWeakPersistent(this)));
   m_visibilityObserver->start();
@@ -4524,13 +4524,16 @@ void FrameView::setNeedsUpdateViewportIntersection() {
 
 void FrameView::updateViewportIntersectionsForSubtree(
     DocumentLifecycle::LifecycleState targetState) {
-  // Notify javascript IntersectionObservers
-  if (targetState == DocumentLifecycle::PaintClean &&
-      frame().document()->intersectionObserverController())
-    frame()
-        .document()
-        ->intersectionObserverController()
-        ->computeTrackedIntersectionObservations();
+  if (targetState == DocumentLifecycle::PaintClean) {
+    recordDeferredLoadingStats();
+    // Notify javascript IntersectionObservers
+    if (frame().document()->intersectionObserverController()) {
+      frame()
+          .document()
+          ->intersectionObserverController()
+          ->computeTrackedIntersectionObservations();
+    }
+  }
 
   if (!m_needsUpdateViewportIntersectionInSubtree)
     return;
@@ -4618,39 +4621,53 @@ void FrameView::updateRenderThrottlingStatus(bool hidden,
 #endif
 }
 
-// TODO(esprehn): Rename this and the method on Document to
-// recordDeferredLoadReason().
-void FrameView::maybeRecordLoadReason() {
+void FrameView::recordDeferredLoadingStats() {
+  if (!frame().document()->frame() || !frame().isCrossOriginSubframe())
+    return;
   FrameView* parent = parentFrameView();
-  if (frame().document()->frame()) {
-    if (!parent) {
-      HTMLFrameOwnerElement* element = frame().deprecatedLocalOwner();
-      if (!element)
-        frame().document()->maybeRecordLoadReason(WouldLoadOutOfProcess);
-      // Having no layout object means the frame is not drawn.
-      else if (!element->layoutObject())
-        frame().document()->maybeRecordLoadReason(WouldLoadDisplayNone);
-    } else {
-      // Assume the main frame has always loaded since we don't track its
-      // visibility.
-      bool parentLoaded =
-          !parent->parentFrameView() ||
-          parent->frame().document()->wouldLoadReason() > Created;
-      // If the parent wasn't loaded, the children won't be either.
-      if (parentLoaded) {
-        if (frameRect().isEmpty())
-          frame().document()->maybeRecordLoadReason(WouldLoadZeroByZero);
-        else if (frameRect().maxY() < 0 && frameRect().maxX() < 0)
-          frame().document()->maybeRecordLoadReason(WouldLoadAboveAndLeft);
-        else if (frameRect().maxY() < 0)
-          frame().document()->maybeRecordLoadReason(WouldLoadAbove);
-        else if (frameRect().maxX() < 0)
-          frame().document()->maybeRecordLoadReason(WouldLoadLeft);
-        else if (!m_hiddenForThrottling)
-          frame().document()->maybeRecordLoadReason(WouldLoadVisible);
-      }
-    }
+  if (!parent) {
+    HTMLFrameOwnerElement* element = frame().deprecatedLocalOwner();
+    // We would fall into an else block on some teardowns and other weird cases.
+    if (!element || !element->layoutObject())
+      frame().document()->recordDeferredLoadReason(WouldLoadNoParent);
+    return;
+  }
+  // Small inaccuracy: frames with origins that match the top level might be
+  // nested in a cross-origin frame. To keep code simpler, count such frames as
+  // WouldLoadVisible, even when their parent is offscreen.
+  WouldLoadReason whyParentLoaded = WouldLoadVisible;
+  if (parent->parentFrameView() && parent->frame().isCrossOriginSubframe())
+    whyParentLoaded = parent->frame().document()->deferredLoadReason();
+
+  // If the parent wasn't loaded, the children won't be either.
+  if (whyParentLoaded == Created)
+    return;
+  // These frames are never meant to be seen so we will need to load them.
+  if (frameRect().isEmpty() || frameRect().maxY() < 0 ||
+      frameRect().maxX() < 0) {
+    frame().document()->recordDeferredLoadReason(whyParentLoaded);
+    return;
   }
+  IntRect parentRect = parent->frameRect();
+  // First clause is checking if the child frame misses its parent laterally.
+  if (frameRect().x() >= parentRect.width() || parentRect.height() <= 0)
+    return;
+
+  int screensAway = frameRect().y() / parentRect.height();

[ojan, 2017/01/18 00:55:01]

Does this need to take scroll position into account? If the user is scrolled
halfway down the page, we need to subtract that from the y() value I think?

Also, the parent isn't necessarily the root for the page, right? I think this
height value does the wrong thing for nested iframes? If I'm reading the
FrameView code right, I think x/y are in absolute coordinates for the whole
page.

So, I think there's two bugs here:
1. If a parent iframe is 2 screens away, and a nested iframe that's 2 screens
away, we'll still load the nested iframe even though it's >3 screens away from
the viewport.
2. If the user scrolls, we don't adjust values appropriately.

I think ultimately, what we want to know is whether this iframe is 1/2/3 screens
away, regardless of nesting, right?

+
+  // We're collecting data for frames that are at most 3 screens away.
+  if (screensAway > 3)
+    return;
+
+  // This means that the top of the child frame is positioned above the parent.
+  // But the above check for maxY() < 0 means that maxY() is positive -> the
+  // child stretches at least into the first screen and possibly lower.
+  if (screensAway < 0)
+    screensAway = 0;
+
+  frame().document()->recordDeferredLoadReason(
+      static_cast<WouldLoadReason>(std::min(static_cast<int>(whyParentLoaded),
+                                            WouldLoadVisible - screensAway)));
 }
 
 bool FrameView::shouldThrottleRendering() const {