Initial implementation of IAccessible2 scrollTo and setTextSelection and

content/browser/accessibility/browser_accessibility.h

Index: content/browser/accessibility/browser_accessibility.h
===================================================================
--- content/browser/accessibility/browser_accessibility.h	(revision 112482)
+++ content/browser/accessibility/browser_accessibility.h	(working copy)
@@ -108,7 +108,46 @@
   // (in global screen coordinates).
   BrowserAccessibility* BrowserAccessibilityForPoint(const gfx::Point& point);
 
+  // Scrolls this element so that the |focus| rect (in local coordinates
+  // relative to this element) is scrolled to fit within the given
+  // |viewport| (which is clipped to the actual bounds of this
+  // object if you specify something larger). If the whole focus area
+  // doesn't fit, you can specify |subfocus|, which will prioritize
+  // a smaller area within |focus|.
+  void ScrollToMakeVisible(const gfx::Rect& subfocus,

[David Tseng, 2011/12/02 00:02:17]

Curious why this isn't taking a more general parameter of BrowserAccessibility
but special cased only for the focused element? It might be useful to check that
|this| is an ancestor of the non-visible element.

Do we need to ever scroll |this| to make visible non-focusable items?

[dmazzoni, 2011/12/03 00:37:10]

Yes - the item to be made visible isn't necessarily focused. Do you have an idea
for a better name for the item rectangle and the sub item rectangle? I used
focus and subfocus in a general sense, not meant to imply that the item must
actually be focused.

I added a comment to clarify, but if you think of another name that's also
concise, we can switch.

+                           const gfx::Rect& focus,
+                           const gfx::Rect& viewport);
+
+  // This is a 1-dimensional scroll offset helper function that's applied
+  // separately in the horizontal and vertical directions, because the
+  // logic is the same.  The goal is to compute the best scroll offset
+  // in order to make a focused item visible within a viewport.
   //
+  // In case the whole focused item cannot fit, you can specify a
+  // subfocus - a smaller region within the focus that should
+  // be prioritized. If the whole focused item can fit, the subfocus is
+  // ignored.
+  //
+  // Example: the viewport is scrolled to the right just enough
+  // that the focus is in view.
+  //   Before:
+  //   +----------Viewport---------+
+  //                         +----Focus---+
+  //                         +--SubFocus--+
+  //
+  //   After:
+  //          +----------Viewport---------+
+  //                         +----Focus---+
+  //                         +--SubFocus--+
+  //
+  // When constraints cannot be fully satistied, the min

[David Tseng, 2011/12/02 00:02:17]

satistied -> satisfied

[dmazzoni, 2011/12/03 00:37:10]

Done.

+  // (left/top) position takes precedence over the max (right/bottom).
+  static int ComputeBestScrollOffset(int current_scroll_offset,
+                                     int subfocus_min, int subfocus_max,
+                                     int focus_min, int focus_max,
+                                     int viewport_min, int viewport_max);
+
+  //
   // Reference counting
   //
   // Each object has an internal reference count and many platform