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

content/browser/accessibility/browser_accessibility.cc

Index: content/browser/accessibility/browser_accessibility.cc
===================================================================
--- content/browser/accessibility/browser_accessibility.cc	(revision 135549)
+++ content/browser/accessibility/browser_accessibility.cc	(working copy)
@@ -15,9 +15,11 @@
 typedef WebAccessibility::IntAttribute IntAttribute;
 typedef WebAccessibility::StringAttribute StringAttribute;
 
-#if (defined(OS_POSIX) && !defined(OS_MACOSX)) || defined(USE_AURA)
-// There's no OS-specific implementation of BrowserAccessibilityManager
-// on Unix, so just instantiate the base class.
+#if !defined(OS_MACOSX) && \
+    !(defined(OS_WIN) && !defined(USE_AURA)) && \
+    !defined(TOOLKIT_GTK)
+// We have subclassess of BrowserAccessibility on Mac, Linux/GTK,
+// and non-Aura Win. For any other platform, instantiate the base class.
 // static
 BrowserAccessibility* BrowserAccessibility::Create() {
   return new BrowserAccessibility();
@@ -202,6 +204,20 @@
   delete this;
 }
 
+#if defined(OS_MACOSX)
+BrowserAccessibilityMac* BrowserAccessibility::ToBrowserAccessibilityMac() {
+  return NULL;
+}
+#elif defined(OS_WIN)
+BrowserAccessibilityWin* BrowserAccessibility::ToBrowserAccessibilityWin() {
+  return NULL;
+}
+#elif defined(TOOLKIT_GTK)
+BrowserAccessibilityGtk* BrowserAccessibility::ToBrowserAccessibilityGtk() {
+  return NULL;
+}
+#endif
+
 bool BrowserAccessibility::GetBoolAttribute(
     BoolAttribute attribute, bool* value) const {
   BoolAttrMap::const_iterator iter = bool_attributes_.find(attribute);