createImageData does not specify rounding behavior for width/height parameters

The IDL for CanvasRenderingContext2D.createImageBitmap specifies that the size parameters are "double", and the functions's algorithm says to take the absolute magnitudes of sw and sh. The behavior for fractional values of sw and sh is unspecified. I looked at open-source implementations of createImageBitmap and it looks like browsers are not compatible.

Blink and webkit:
effective width = ceil(abs(sw))

Mozilla: effective width = abs(toInt32(sw)), which simplifies to floor(abs(sw))

Sources:
https://trac.webkit.org/browser/trunk/Source/WebCore/html/canvas/CanvasRenderingContext2D.cpp#L2017
https://dxr.mozilla.org/mozilla-central/source/dom/canvas/CanvasRenderingContext2D.cpp#5559
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit/Source/modules/canvas2d/BaseRenderingContext2D.cpp&sq=package:chromium&type=cs&l=1148

Would be nice to agree on what the interoperable behavior should be, then spec it.

Review the createImageBitmap IDL and algorithm alongside the Blink, WebKit, and Mozilla implementation sources linked in the issue. Compare their fractional sw and sh handling, then establish and specify interoperable rounding behavior once the standards discussion reaches agreement.