Bug 961783. Remove unneeded DDB optimization. r=vlad

As far as I can tell we always draw images to dc's that are in system memory.
In this case there's no upside to having ddb and a potential downside because
we have to do a readback from gpu into system memory.

--HG--
extra : rebase_source : e536721adc1de2bcff3300ee29c2d1c4b8c15ac0
Bug 958363. Turn an error into a warning in gfxBlur. r=mattwoodrow
Bug 952977: Convert CreateMatrix to gfx::Matrix r=nical
Bug 952782 - Use nsIDocument instead of nsIDOMDocument in accessible r=tbsaunde, bz
Bug 961354 part 1: Move nsCSSOffsetState constructor definition to .cpp file. r=mats
Bug 961354 part 2: Don't consider absolutely-positioned elements to be flex items, since they don't participate in normal flex layout. r=mats
Bug 961760: Remove a bunch of unused Chromium IPC code. r=bent
Bug 924972 - Wait for focus before running test_reftests_with_caret.html and also focus the iframe inside the test properly; r=Enn
Bug 953381 - Add generic support for casting a video to a second screen service r=wesj
Bug 953381 - video discovery tests r=wesj
Bug 953381 - Move CastingApps into a separate JS file r=wesj
Bug 953381 - Basic media casting control bar r=wesj
Backed out changeset 1e7ec87921a5 (debugging patch for bug 924972) because it's no longer needed

--HG--
extra : rebase_source : 311a86827be79de56abd61e48bac0c3268b891bb
Bug 916350 - Make it possible to run reftests on b2g desktop, r=jgriffin,ted
Bug 888534: Add missing operations to IOInterposer::Unregister; r=jonasfj
Bug 959531 - More about:home testing (r=felipe)
Bug 961318 - Tweak off-main-thread parsing heuristic to avoid delaying execution when an atoms-zone GC is in progress (r=billm)

--HG--
extra : rebase_source : bd4e6b296e7a02dbe2370a515174dcd1a6a57ffa
Bug 961841 - use Services.obs for the observer service in BrowserElementPanning.js; r=smaug
Backout aa955afe7507:49f1c6fa27f8 (bug 953381) for robocop orange on this CLOSED TREE
Backout 2c24dc80aa00 (bug 916350) for Android reftest/crashtest orange on this CLOSED TREE