Get rid of extraneous accessibility tree traversal code.

(Re-land) Get rid of extraneous accessibility tree traversal code.

We never used AccessibilityRenderObject::previousSibling, and
I've been scared for a long time someone would accidentally
use it and we'd discover it's full of bugs, since it had no
test coverage. (Several bugs have been caught in nextSibling over
the years.) Time for it to die.

We also don't need AccessibilityObject::lastChild, though
the implementation was trivial.

The public interface needs even less - we can get rid of
firstChild, lastChild, nextSibling, and previousSibling,
because childAt is the only one called.

BUG=247082
R=eseidel@chromium.org, jamesr@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=152005

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=152050

[dmazzoni, 2013-06-06 06:59:32]

jamesr: please review public api change

[eseidel, 2013-06-06 08:57:38]

lgtm

Fantastic!

[jamesr, 2013-06-06 17:12:05]

lgtm

[commit-bot: I haz the power, 2013-06-06 17:15:34]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/dmazzoni@chromium.org/16361013/1

[commit-bot: I haz the power, 2013-06-06 17:15:37]

Failed to apply patch for
Source/WebKit/chromium/public/WebAccessibilityObject.h:
While running patch -p1 --forward --force --no-backup-if-mismatch;
  patching file Source/WebKit/chromium/public/WebAccessibilityObject.h
  Hunk #1 FAILED at 92.
  1 out of 1 hunk FAILED -- saving rejects to file
Source/WebKit/chromium/public/WebAccessibilityObject.h.rej

Patch:       Source/WebKit/chromium/public/WebAccessibilityObject.h
Index: Source/WebKit/chromium/public/WebAccessibilityObject.h
diff --git a/Source/WebKit/chromium/public/WebAccessibilityObject.h
b/Source/WebKit/chromium/public/WebAccessibilityObject.h
index
812f49b1dd81bf42f00de8c487790eebc370148b..de7d3297ed8796b7d33b2e6b6fa1a2e4505cf2a1
100644
--- a/Source/WebKit/chromium/public/WebAccessibilityObject.h
+++ b/Source/WebKit/chromium/public/WebAccessibilityObject.h
@@ -92,12 +92,7 @@ public:
     WEBKIT_EXPORT unsigned childCount() const;
 
     WEBKIT_EXPORT WebAccessibilityObject childAt(unsigned) const;
-    WEBKIT_EXPORT WebAccessibilityObject firstChild() const;
-    WEBKIT_EXPORT WebAccessibilityObject focusedChild() const;
-    WEBKIT_EXPORT WebAccessibilityObject lastChild() const;
-    WEBKIT_EXPORT WebAccessibilityObject nextSibling() const;
     WEBKIT_EXPORT WebAccessibilityObject parentObject() const;
-    WEBKIT_EXPORT WebAccessibilityObject previousSibling() const;
 
     WEBKIT_EXPORT bool isAnchor() const;
     WEBKIT_EXPORT bool isAriaReadOnly() const;

[commit-bot: I haz the power, 2013-06-06 20:53:45]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/dmazzoni@chromium.org/16361013/6002

[commit-bot: I haz the power, 2013-06-07 01:20:17]

Retried try job too often on win_layout_rel for step(s) webkit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_layout...

[commit-bot: I haz the power, 2013-06-07 02:21:23]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/dmazzoni@chromium.org/16361013/6002

[dmazzoni, 2013-06-07 07:47:51]

Committed patchset #3 manually as r152005 (presubmit successful).

[commit-bot: I haz the power, 2013-06-07 19:43:11]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/dmazzoni@chromium.org/16361013/26001

[commit-bot: I haz the power, 2013-06-07 21:30:58]

Change committed as 152050