Dropdown button aria attributes

app/src/ui/dropdown-select-button.tsx

@@ -31,6 +31,9 @@ interface IDropdownSelectButtonProps<T extends string> {
   /** tooltip for the button */
   readonly tooltip?: string
 
+   /** aria label for the button */
+   readonly dropdownAriaLabel: string
+
   /** Callback for when the button selection changes*/
   readonly onCheckedOptionChange?: (
     selectedOption: IDropdownSelectButtonOption<T>
@@ -237,7 +240,7 @@ export class DropdownSelectButton<
   }
 
   public render() {
-    const { options, disabled } = this.props
+    const { options, disabled, dropdownAriaLabel } = this.props
     const {
       checkedOption: selectedOption,
       optionsPositionBottom,
@@ -274,6 +277,9 @@ export class DropdownSelectButton<
             className={dropdownClasses}
             onClick={this.openSplitButtonDropdown}
             type="button"
+            ariaExpanded={showButtonOptions}
+            ariaHaspopup={true}
+            ariaLabel={dropdownAriaLabel}
           >
             <Octicon symbol={OcticonSymbol.triangleDown} />
           </Button>

app/src/ui/history/merge-call-to-action-with-conflicts.tsx

@@ -183,6 +183,7 @@ export class MergeCallToActionWithConflicts extends React.Component<
         <DropdownSelectButton
           checkedOption={this.state.selectedOperation}
           options={getMergeOptions()}
+          dropdownAriaLabel="Merge options"
           disabled={disabled}
           onCheckedOptionChange={this.onOperationChange}
           onSubmit={this.onOperationInvoked}

app/src/ui/multi-commit-operation/choose-branch/base-choose-branch-dialog.tsx

@@ -243,6 +243,7 @@ export abstract class BaseChooseBranchDialog extends React.Component<
             checkedOption={operation}
             options={getMergeOptions()}
             disabled={!this.canStart()}
+            dropdownAriaLabel="Merge options"
             tooltip={this.getSubmitButtonToolTip()}
             onCheckedOptionChange={this.onOperationChange}
           />

app/src/ui/suggested-actions/dropdown-suggested-action.tsx

@@ -162,6 +162,7 @@ export class DropdownSuggestedAction<T extends string> extends React.Component<
             value,
           }))}
           disabled={disabled}
+          dropdownAriaLabel="Suggested actions for this branch"
           onCheckedOptionChange={this.onActionSelectionChange}
           onSubmit={this.onActionSubmitted}
         />