Bug 1390342 - Skip pattern matching in HasPatternMismatch() if @pattern is not set. r=ehsan

We use a bitfield in HTMLInputElement to cache whether the input element has the
@pattern set, and skip pattern mathching in HasPatternMismatch() if the
attribute is not set.

dom/html/HTMLInputElement.h

@@ -339,6 +339,11 @@ public:
     return mSelectionProperties;
   }
 
+  bool HasPatternAttribute() const
+  {
+    return mHasPatternAttribute;
+  }
+
   // nsIConstraintValidation
   bool     IsTooLong();
   bool     IsTooShort();
@@ -1667,6 +1672,7 @@ protected:
   bool                     mPickerRunning : 1;
   bool                     mSelectionCached : 1;
   bool                     mIsPreviewEnabled : 1;
+  bool                     mHasPatternAttribute : 1;
 
 private:
   static void MapAttributesIntoRule(const nsMappedAttributes* aAttributes,