IntersectionObserver: Always send an initial notification.

third_party/WebKit/Source/core/dom/IntersectionObservation.h

Index: third_party/WebKit/Source/core/dom/IntersectionObservation.h
diff --git a/third_party/WebKit/Source/core/dom/IntersectionObservation.h b/third_party/WebKit/Source/core/dom/IntersectionObservation.h
index dcb93231cd50f05f279f81ac5504dec7895bad55..e3f1dd433fcb8e72b71eb92e04b67b27b63462af 100644
--- a/third_party/WebKit/Source/core/dom/IntersectionObservation.h
+++ b/third_party/WebKit/Source/core/dom/IntersectionObservation.h
@@ -23,7 +23,7 @@ class IntersectionObservation final
   IntersectionObserver* observer() const { return m_observer.get(); }
   Element* target() const { return m_target; }
   unsigned lastThresholdIndex() const { return m_lastThresholdIndex; }
-  void setLastThresholdIndex(unsigned index) { m_lastThresholdIndex = index; }
+  void setLastThresholdIndex(int index) { m_lastThresholdIndex = index; }

[ojan, 2017/01/26 01:44:56]

I assume this is leftover from a previous iteration of the patch?

[szager1, 2017/01/30 19:37:41]

Yep, thanks for the catch.

   void computeIntersectionObservations(DOMHighResTimeStamp);
   void disconnect();
 
@@ -34,7 +34,12 @@ class IntersectionObservation final
   WeakMember<Element> m_target;
 
   const unsigned m_shouldReportRootBounds : 1;
+
+  // HACK: the spec calls for the inital value of m_lastThresholdIndex to be
+  // -1.  But if m_lastThresholdIndex is changed to a signed int type, then
+  // we can't bit-pack it.  Instead, inflate all thresholdIndex values by 1.

[ojan, 2017/01/26 01:44:56]

Since we're going hacky, how about initializing m_lastThresholdIndex to
0x40000000 and leaving the rest of the code untouched? Then the hack is
localized to one place and there's no need for a RELEASE_ASSERT.

[szager1, 2017/01/30 19:37:41]

The RELEASE_ASSERT is me being paranoid.  This patch doesn't make it any more
necessary than it was before; it just occurred to me that guarding against
overflow is probably a good idea.

0x40000000 doesn't fit in 30 bits.  I could initialize it to
kMaxThresholdIndex-1, if you think that's clearer.

   unsigned m_lastThresholdIndex : 30;
+  static const unsigned kMaxThresholdIndex = (unsigned)0x40000000;
 };
 
 }  // namespace blink