Expose aria-pressed as STATE_SYSTEM_PRESSED on windows

According to specs http://rawgit.com/w3c/aria/master/core-aam/core-aam.html

aria-pressed {true, mixed} should set STATE_SYSTEM_PRESSED and false should
clear STATE_SYSTEM_PRESSED

This CL depends on https://codereview.chromium.org/767183002/

BUG=171625

Review URL: https://codereview.chromium.org/771583002

Cr-Commit-Position: refs/heads/master@{#308073}

content/browser/accessibility/browser_accessibility_win.cc

@@ -3412,14 +3412,6 @@ void BrowserAccessibilityWin::InitRoleAndState() {
       break;
     case ui::AX_ROLE_BUTTON:
       ia_role_ = ROLE_SYSTEM_PUSHBUTTON;
-      bool is_aria_pressed_defined;
-      bool is_mixed;
-      if (GetAriaTristate("aria-pressed", &is_aria_pressed_defined, &is_mixed))
-        ia_state_ |= STATE_SYSTEM_PRESSED;
-      if (is_aria_pressed_defined)
-        ia2_role_ = IA2_ROLE_TOGGLE_BUTTON;
-      if (is_mixed)
-        ia_state_ |= STATE_SYSTEM_MIXED;
       break;
     case ui::AX_ROLE_CANVAS:
       if (GetBoolAttribute(ui::AX_ATTR_CANVAS_HAS_FALLBACK)) {

content/test/data/accessibility/aria-button-expected-win.txt

-#<skip - http://crbug.com/171625>
 ROLE_SYSTEM_DOCUMENT READONLY FOCUSABLE
-    ROLE_SYSTEM_PUSHBUTTON xml-roles:button
-    IA2_ROLE_TOGGLE_BUTTON xml-roles:button PRESSED checkable:true
-    IA2_ROLE_TOGGLE_BUTTON xml-roles:button checkable:true
-    ROLE_SYSTEM_BUTTONMENU HASPOPUP xml-roles:button
-    ROLE_SYSTEM_PUSHBUTTON xml-roles:button
+    ROLE_SYSTEM_PUSHBUTTON FOCUSABLE xml-roles:button
+    IA2_ROLE_TOGGLE_BUTTON PRESSED FOCUSABLE xml-roles:button checkable:true
+    IA2_ROLE_TOGGLE_BUTTON FOCUSABLE xml-roles:button checkable:true
+    ROLE_SYSTEM_BUTTONMENU FOCUSABLE HASPOPUP xml-roles:button
+    ROLE_SYSTEM_PUSHBUTTON FOCUSABLE xml-roles:button

content/test/data/accessibility/aria-pressed-expected-win.txt

-#<skip - PRESSED not set: http://crbug.com/171625>
 ROLE_SYSTEM_DOCUMENT READONLY FOCUSABLE
     ROLE_SYSTEM_PUSHBUTTON FOCUSABLE
     IA2_ROLE_TOGGLE_BUTTON FOCUSABLE checkable:true
-    IA2_ROLE_TOGGLE_BUTTON FOCUSABLE PRESSED checkable:true
-    IA2_ROLE_TOGGLE_BUTTON FOCUSABLE PRESSED checkable:true
+    IA2_ROLE_TOGGLE_BUTTON PRESSED FOCUSABLE checkable:true
+    IA2_ROLE_TOGGLE_BUTTON PRESSED FOCUSABLE checkable:true