Bug 1449019. Actually propagate out exceptions from the innerHTML getter. r=smaug

I moved the IgnoreErrors decl so it would come after the OOMReporter decl and I
could add the new conversion operator.

MozReview-Commit-ID: B1S6DXmZfvE

dom/html/HTMLScriptElement.h

@@ -27,7 +27,7 @@ public:
   // nsISupports
   NS_DECL_ISUPPORTS_INHERITED
 
-  NS_IMETHOD GetInnerHTML(nsAString& aInnerHTML) override;
+  void GetInnerHTML(nsAString& aInnerHTML, OOMReporter& aError) override;
   virtual void SetInnerHTML(const nsAString& aInnerHTML,
                             nsIPrincipal* aSubjectPrincipal,
                             mozilla::ErrorResult& aError) override;