Bug 1343037 part 12. Implement nsTextEditorState::SetSelectionStart. r=ehsan

This introduces three behavior changes:

1)  Before this change, in cached mode, we did not enforce the "start <= end"
    invariant.
2)  Before this change, in cached mode, we did not fire "select" events on
    selectionStart changes.
3)  Changes the IDL type of HTMLInputElement's selectionStart attribute to
    "unsigned long" to match the spec and HTMLTextareaElement.

MozReview-Commit-ID: JM9XXMMPUHM

dom/html/nsTextEditorState.cpp

@@ -1708,6 +1708,35 @@ nsTextEditorState::SetSelectionRange(int32_t aStart, int32_t aEnd,
   }
 }
 
+void
+nsTextEditorState::SetSelectionStart(const mozilla::dom::Nullable<uint32_t>& aStart,
+                                     ErrorResult& aRv)
+{
+  int32_t start = 0;
+  if (!aStart.IsNull()) {
+    // XXXbz This will do the wrong thing for input values that are out of the
+    // int32_t range...
+    start = aStart.Value();
+  }
+
+  int32_t ignored, end;
+  GetSelectionRange(&ignored, &end, aRv);
+  if (aRv.Failed()) {
+    return;
+  }
+
+  nsITextControlFrame::SelectionDirection dir = GetSelectionDirection(aRv);
+  if (aRv.Failed()) {
+    return;
+  }
+
+  if (end < start) {
+    end = start;
+  }
+
+  SetSelectionRange(start, end, dir, aRv);
+}
+
 HTMLInputElement*
 nsTextEditorState::GetParentNumberControl(nsFrame* aFrame) const
 {