Cleanup/Speedup Montage.defineProperty()

[marchant]

By bypassing Object.defineProperty() when possible

[hthetiot]

core/core.js: line 435, col 17, Misleading line break before '?'; readers may interpret this as an expression boundary.
core/core.js: line 446, col 13, Expected '{' and instead saw 'descriptor'.
core/core.js: line 455, col 21, Misleading line break before '?'; readers may interpret this as an expression boundary.
core/core.js: line 457, col 25, Misleading line break before '?'; readers may interpret this as an expression boundary.
core/core.js: line 458, col 29, Misleading line break before '?'; readers may interpret this as an expression boundary.

[hthetiot]

Chromium 60.0.3112 (Ubuntu 0.0.0) flow/flow ui/flow/flow-spec Flow handling resize after flow changes in size should update frustum culling and iterations FAILED
	Expected '0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50' to be '0 1'.
	    at eval (test/spec/ui/flow-spec.js:124:74)
	    at r (node_modules/bluebird/js/browser/bluebird.min.js:31:9004)
	    at i._settlePromiseFromHandler (node_modules/bluebird/js/browser/bluebird.min.js:30:14217)
	    at i._settlePromise (node_modules/bluebird/js/browser/bluebird.min.js:30:15020)
	    at i._settlePromise0 (node_modules/bluebird/js/browser/bluebird.min.js:30:15721)
	    at i._settlePromises (node_modules/bluebird/js/browser/bluebird.min.js:30:17051)
	    at r._drainQueue (node_modules/bluebird/js/browser/bluebird.min.js:29:3056)
	    at r._drainQueues (node_modules/bluebird/js/browser/bluebird.min.js:29:3117)
	    at drainQueues (node_modules/bluebird/js/browser/bluebird.min.js:29:1238)
	    at <anonymous>
	Expected 51 to be 2.
	    at eval (test/spec/ui/flow-spec.js:125:72)
	    at r (node_modules/bluebird/js/browser/bluebird.min.js:31:9004)
	    at i._settlePromiseFromHandler (node_modules/bluebird/js/browser/bluebird.min.js:30:14217)
	    at i._settlePromise (node_modules/bluebird/js/browser/bluebird.min.js:30:15020)
	    at i._settlePromise0 (node_modules/bluebird/js/browser/bluebird.min.js:30:15721)
	    at i._settlePromises (node_modules/bluebird/js/browser/bluebird.min.js:30:17051)
	    at r._drainQueue (node_modules/bluebird/js/browser/bluebird.min.js:29:3056)
	    at r._drainQueues (node_modules/bluebird/js/browser/bluebird.min.js:29:3117)
	    at drainQueues (node_modules/bluebird/js/browser/bluebird.min.js:29:1238)
	    at <anonymous>

cc @marchant that the travis errors

[hthetiot]

Fail integration test, moved to next release window.