Bug 1683426. Assert in DManipEventHandler::OnContentUpdated that SendPinch returns true if mShouldSendPinchStart is true. r=botond

Otherwise we wouldn't send a pinch start. This should never be hit because if we get here the current scale should not be fuzzy equal to the previous scale so SendPinch should compute a non-zero deltaY and send an event and return true.

Differential Revision: https://phabricator.services.mozilla.com/D100170

widget/windows/DirectManipulationOwner.cpp

@@ -325,6 +325,9 @@ DManipEventHandler::OnContentUpdated(IDirectManipulationViewport* viewport,
   } else if (mState == State::ePinching) {
     if (mShouldSendPinchStart) {
       updateLastScale = SendPinch(Phase::eStart, scale);
+      // If we get here our current scale is not fuzzy equal to the previous
+      // scale, so SendPinch should return true.
+      MOZ_ASSERT(updateLastScale);
       mShouldSendPinchStart = false;
     } else {
       updateLastScale = SendPinch(Phase::eMiddle, scale);