Add initial GTK web accessibility framework (new with valgrind fix).

content/browser/accessibility/browser_accessibility.h

Index: content/browser/accessibility/browser_accessibility.h
===================================================================
--- content/browser/accessibility/browser_accessibility.h	(revision 135549)
+++ content/browser/accessibility/browser_accessibility.h	(working copy)
@@ -16,10 +16,12 @@
 #include "webkit/glue/webaccessibility.h"
 
 class BrowserAccessibilityManager;
-#if defined(OS_MACOSX) && __OBJC__
-@class BrowserAccessibilityCocoa;
+#if defined(OS_MACOSX)
+class BrowserAccessibilityMac;
 #elif defined(OS_WIN)
 class BrowserAccessibilityWin;
+#elif defined(TOOLKIT_GTK)
+class BrowserAccessibilityGtk;
 #endif
 
 using webkit_glue::WebAccessibility;
@@ -187,10 +189,12 @@
   bool instance_active() const { return instance_active_; }
   int32 ref_count() const { return ref_count_; }
 
-#if defined(OS_MACOSX) && __OBJC__
-  BrowserAccessibilityCocoa* toBrowserAccessibilityCocoa();
+#if defined(OS_MACOSX)
+  virtual BrowserAccessibilityMac* ToBrowserAccessibilityMac();
 #elif defined(OS_WIN)
-  BrowserAccessibilityWin* toBrowserAccessibilityWin();
+  virtual BrowserAccessibilityWin* ToBrowserAccessibilityWin();
+#elif defined(TOOLKIT_GTK)
+  virtual BrowserAccessibilityGtk* ToBrowserAccessibilityGtk();
 #endif
 
   // Retrieve the value of a bool attribute from the bool attribute