Bug 1289432 - Switch over to using the mActiveXXXBlock in some places instead...

Bug 1289432 - Switch over to using the mActiveXXXBlock in some places instead of fishing around in mInputBlockQueue. r=botond

Note that this patch has a subtle functional change because the mActiveXXXBlock
variables can remain non-null even if there are no blocks in mInputBlockQueue.
In fact, this patch contains the secret sauce that allows the input queue to
handle interleaved input events, because this ensures that the interleaved events
end up getting associated with the pre-existing active block rather than creating
a new one.

MozReview-Commit-ID: 7GkbSe9IaC4

gfx/layers/apz/src/InputQueue.cpp

@@ -94,13 +94,13 @@ InputQueue::ReceiveTouchInput(const RefPtr<AsyncPanZoomController>& aTarget,
     bool haveBehaviors = false;
     if (!gfxPrefs::TouchActionEnabled()) {
       haveBehaviors = true;
-    } else if (!mInputBlockQueue.IsEmpty() && CurrentBlock()->AsTouchBlock()) {
-      haveBehaviors = CurrentTouchBlock()->GetAllowedTouchBehaviors(currentBehaviors);
+    } else if (mActiveTouchBlock) {
+      haveBehaviors = mActiveTouchBlock->GetAllowedTouchBehaviors(currentBehaviors);
       // If the behaviours aren't set, but the main-thread response timer on
       // the block is expired we still treat it as though it has behaviors,
       // because in that case we still want to interrupt the fast-fling and
       // use the default behaviours.
-      haveBehaviors |= CurrentTouchBlock()->IsContentResponseTimerExpired();
+      haveBehaviors |= mActiveTouchBlock->IsContentResponseTimerExpired();
     }
 
     block = StartNewTouchBlock(aTarget, aTargetConfirmed, false);
@@ -132,10 +132,7 @@ InputQueue::ReceiveTouchInput(const RefPtr<AsyncPanZoomController>& aTarget,
 
     MaybeRequestContentResponse(aTarget, block);
   } else {
-    if (!mInputBlockQueue.IsEmpty()) {
-      block = mInputBlockQueue.LastElement().get()->AsTouchBlock();
-    }
-
+    block = mActiveTouchBlock.get();
     if (!block) {
       NS_WARNING("Received a non-start touch event while no touch blocks active!");
       return nsEventStatus_eIgnore;
@@ -189,11 +186,7 @@ InputQueue::ReceiveMouseInput(const RefPtr<AsyncPanZoomController>& aTarget,
   // with a new target.
   bool newBlock = DragTracker::StartsDrag(aEvent);
 
-  DragBlockState* block = nullptr;
-  if (!newBlock && !mInputBlockQueue.IsEmpty()) {
-    block = mInputBlockQueue.LastElement()->AsDragBlock();
-  }
-
+  DragBlockState* block = newBlock ? nullptr : mActiveDragBlock.get();
   if (block && block->HasReceivedMouseUp()) {
     block = nullptr;
   }
@@ -252,18 +245,14 @@ InputQueue::ReceiveScrollWheelInput(const RefPtr<AsyncPanZoomController>& aTarge
                                     bool aTargetConfirmed,
                                     const ScrollWheelInput& aEvent,
                                     uint64_t* aOutInputBlockId) {
-  WheelBlockState* block = nullptr;
-  if (!mInputBlockQueue.IsEmpty()) {
-    block = mInputBlockQueue.LastElement()->AsWheelBlock();
-
-    // If the block is not accepting new events we'll create a new input block
-    // (and therefore a new wheel transaction).
-    if (block &&
-        (!block->ShouldAcceptNewEvent() ||
-         block->MaybeTimeout(aEvent)))
-    {
-      block = nullptr;
-    }
+  WheelBlockState* block = mActiveWheelBlock.get();
+  // If the block is not accepting new events we'll create a new input block
+  // (and therefore a new wheel transaction).
+  if (block &&
+      (!block->ShouldAcceptNewEvent() ||
+       block->MaybeTimeout(aEvent)))
+  {
+    block = nullptr;
   }
 
   MOZ_ASSERT(!block || block->InTransaction());
@@ -327,9 +316,8 @@ InputQueue::ReceivePanGestureInput(const RefPtr<AsyncPanZoomController>& aTarget
   }
 
   PanGestureBlockState* block = nullptr;
-  if (!mInputBlockQueue.IsEmpty() &&
-      aEvent.mType != PanGestureInput::PANGESTURE_START) {
-    block = mInputBlockQueue.LastElement()->AsPanGestureBlock();
+  if (aEvent.mType != PanGestureInput::PANGESTURE_START) {
+    block = mActivePanGestureBlock.get();
   }
 
   PanGestureInput event = aEvent;
@@ -525,10 +513,7 @@ InputQueue::CurrentPanGestureBlock() const
 WheelBlockState*
 InputQueue::GetCurrentWheelTransaction() const
 {
-  if (mInputBlockQueue.IsEmpty()) {
-    return nullptr;
-  }
-  WheelBlockState* block = CurrentBlock()->AsWheelBlock();
+  WheelBlockState* block = mActiveWheelBlock.get();
   if (!block || !block->InTransaction()) {
     return nullptr;
   }