Add support for the object-position CSS property.

Add support for the object-position CSS property.

This is hidden behind an "experimental" runtime flag named
"ObjectFitPosition", together with object-fit.

This is an implementation of object-position as described in
http://www.w3.org/TR/2012/CR-css3-images-20120417/#object-position

Object-position is used to offset replaced content within its content
box. Painting is always clipped against the content box, regardless of
the "overflow" property. This property is useful together with
object-fit (to achieve a difference between content box size and
replaced content size, so that specifying alignment is interesting),
but can also be used on its own.

BUG=236333
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=158155

[mstensho (USE GERRIT), 2013-09-20 15:43:20]

This is another attempt to land object-position. It's a continuation of
https://codereview.chromium.org/22839023/ (the last patch there should be
identical to the first patch here), which was reverted because it introduced
assertion failures.

[ojan, 2013-09-20 20:18:06]

lgtm

[commit-bot: I haz the power, 2013-09-20 20:21:47]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/mstensho@opera.com/24077007/6001

[commit-bot: I haz the power, 2013-09-20 20:22:04]

Failed to apply patch for Source/core/page/UseCounter.cpp:
While running patch -p1 --forward --force --no-backup-if-mismatch;
  patching file Source/core/page/UseCounter.cpp
  Hunk #1 FAILED at 495.
  Hunk #2 succeeded at 510 (offset 1 line).
  1 out of 2 hunks FAILED -- saving rejects to file
Source/core/page/UseCounter.cpp.rej

Patch:       Source/core/page/UseCounter.cpp
Index: Source/core/page/UseCounter.cpp
diff --git a/Source/core/page/UseCounter.cpp b/Source/core/page/UseCounter.cpp
index
5db2ae9ea987d0ab5a34cb6b64c75556c12c63d7..75b87e777e27e5d2de82e9aeb3e11dcc05751cd0
100644
--- a/Source/core/page/UseCounter.cpp
+++ b/Source/core/page/UseCounter.cpp
@@ -495,6 +495,7 @@ int
UseCounter::mapCSSPropertyIdToCSSSampleIdForHistogram(int id)
     case CSSPropertyObjectFit: return 433;
     case CSSPropertyPaintOrder: return 434;
     case CSSPropertyMaskSourceType: return 435;
+    case CSSPropertyObjectPosition: return 436;
 
     // Add new features above this line (don't change the assigned numbers of
the existing
     // items) and update maximumCSSSampleId() with the new maximum value.
@@ -509,7 +510,7 @@ int
UseCounter::mapCSSPropertyIdToCSSSampleIdForHistogram(int id)
     return 0;
 }
 
-static int maximumCSSSampleId() { return 434; }
+static int maximumCSSSampleId() { return 436; }
 
 UseCounter::UseCounter()
 {

[commit-bot: I haz the power, 2013-09-20 21:51:38]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/mstensho@opera.com/24077007/13001

[commit-bot: I haz the power, 2013-09-21 04:25:26]

Change committed as 158155