Have Document::topDocument() return a reference

Have Document::topDocument() return a reference

Have Document::topDocument() return a reference instead of a pointer as it can
never return null. This makes the calling code look safer.

R=adamk

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=167922

[adamk, 2014-02-26 17:30:51]

lgtm

https://codereview.chromium.org/179163004/diff/1/Source/core/accessibility/AX...
File Source/core/accessibility/AXObjectCache.cpp (left):

https://codereview.chromium.org/179163004/diff/1/Source/core/accessibility/AX...
Source/core/accessibility/AXObjectCache.cpp:113: m_document =
const_cast<Document*>(doc);
Ha! Thanks for getting rid of this const_cast

[adamk, 2014-02-26 17:31:05]

The CQ bit was checked by adamk@chromium.org

[commit-bot: I haz the power, 2014-02-26 17:31:13]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ch.dumez@samsung.com/179163004/1

[commit-bot: I haz the power, 2014-02-26 19:39:29]

Change committed as 167922