Bug 878875 - Import PannerNode tests from Blink. r=ehsan

Imported from Blink SVN revision 152035
Bug 878875 - Port Blink's LayoutTest for PannerNode to mochitest-plain. r=ehsan
Bug 880392 - Fix use-after free with exact rooting in XPCShell; r=sfink

--HG--
extra : rebase_source : a509e84b7165b8a40f4a06e006dfc614665eef2c
Bug 798438 - Use a dictionary to set context options instead of an nsIPropertyBag r=bz
Bug 879998 - Remove some dead code in content/events r=smaug
Backout 498f79c24e70 (bug 860560) for browser-chrome bustage