Bug 1102304 - Fix crash in 32 bit mode on 10.10 by correcting the _addKnownSubview signature. r=smichaud

This just copies the definition for the documented -[NSView addSubview:positioned:relativeTo:] method, which is the exact counterpart of this (undocumented) method. Using "long long" for the positioned: argument was wrong - the real type is NSWindowOrderingMode, which is typedefed to NSInteger, which is pointer-sized and thus doesn't match long long on 32 bit.
Bug 907396 - Style system support for display:contents.  r=dbaron
Bug 907396 - Flex/Grid container changes for display:contents.  r=dholbert
Bug 907396 - Put display:contents support behind a pref - disabled by default.  r=dholbert
Bug 907396 - Frame manager support for display:contents.  r=bzbarsky
Bug 907396 - Frame constructor changes for display:contents.  r=bzbarsky
Bug 907396 - Implement RestyleUndisplayedDescendants that restyles diplay:none children and display:contents descendants.  r=bzbarsky
Bug 907396 - Replace GetParentStyleContextFrame with GetParentStyleContext which can return frame-less display:contents style contexts.  r=bzbarsky
Bug 907396 - Make RestyleManager::RestyleElement and nsCSSFrameConstructor::MaybeRecreateFramesForElement deal with display:contents elements.  r=bzbarsky
Bug 907396 - DEBUG only; make frame tree dumps print up to 2 style context parents in the unusual case when they are not the parent frame's style context (e.g. display:contents).  r=bzbarsky
Bug 907396 - Tests for CSS 'display:contents'.