Much as I would have liked it if the last blocker about having to clobber every few pushes would have solved all our problems, it didn't. https://hg.mozilla.org/integration/mozilla-inbound/rev/f26d6c5a2d93 failed in opt and debug Linux64 mochitest-1 and reftests in https://tbpl.mozilla.org/?tree=Mozilla-Inbound&rev=f26d6c5a2d93 and debug Linux64 in https://tbpl.mozilla.org/?tree=Mozilla-Inbound&rev=b8893f7f80c5 before starting to pass. I retriggered the builds on its landing push after clobbering, but I already know what the results will be, the clobber will have "fixed" it.
This should be fixed by the backout of bug 781529. When building nsCanvasRenderingContext2D.cpp with -MMD, the .deps/nsCanvasRenderingContext2D.o.pp file doesn't contain a reference to ImageContainer.h. With -MD it does. AFAICT, ImageContainer.h is never declared as a system header, so this likely is a GCC bug.