Changes in 20191222094212

Built from 9e60c8fbb6ec7adf45ea9da54b384b96bbee2fae

..index..
Bug 1605321 R[Core:DOM: Core & HTML]Perma fission TEST-UNEXPECTED-TIMEOUT | /html/browsers/the-window-object/apis-for-creating-and-navigating-browsing-contexts-by-name/no_window_open_when_term_nesting_level_nonzero.window.html | Executor hit external timeout (this may indicate a hang)
Bug 1603074 R[Core:DOM: Drag & Drop]Improve `synthesizePlainDragAndDrop()` in EventUtils.js
Bug 1597829 R[Core:DOM: Editor]Before inserting drag and drop content, corresponding editing host or text control element should be focused
Bug 1605554 R[Core:Graphics]Use after free in GetSkImageForSurface
Bug 1590350 R[Core:MathML]Refresh telemetry probe for MathML.
Bug 1602410 R[Core:Printing: Setup]Make `window.print()` invoke printing via the parent process using an IPDL actor
Bug 1605129 R[Core:Web Replay]Perma [tier2] devtools/client/webreplay/mochitest/browser_dbg_rr_breakpoints-07.js | Test timed out -
Bug 1605560 R[Firefox Build System:General]Move to clang 9.0.1
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Changes to 8 bugs - 7 fixed.