Autofill: Use field maxlength to improve credit card date matching.

chrome/test/data/autofill/heuristics/input/bug_471748.html

Index: chrome/test/data/autofill/heuristics/input/bug_471748.html
diff --git a/chrome/test/data/autofill/heuristics/input/bug_471748.html b/chrome/test/data/autofill/heuristics/input/bug_471748.html
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+<div class="pay_method">
+  <h3 class="h_check">Pay with Credit Card:</h3>
+
+  <div class="saved_wrap clearfix">
+
+  </div>
+
+  <div id="fade_card">
+    <div class="cc_row card_type cf">
+      <label for="cctype">Card Type:</label>
+      <div class="cc_selwrap">
+        <div class="dropdownbox"><div class="current_selection"><span class="selection_text" title="Visa">Visa</span><span class="drop_arrow"><span></span></span></div><ul class="optionslist"><li class="option selected">Visa</li><li class="option">MasterCard</li><li class="option">American Express</li><li class="option">Discover</li></ul></div><select name="ccType" id="cctype" class="fancy_select" style="display: none;">
+          <option value="VISA" selected="">Visa</option>
+          <option value="MASTERCARD">MasterCard</option>
+          <option value="AMEX">American Express</option>
+          <option value="DISCOVER">Discover</option>
+        </select>
+      </div>
+      <div class="cc_iconwrap">
+        <span class="cc_icon ic_visa selected">Visa</span>
+        <span class="cc_icon ic_mc">MasterCard</span>
+        <span class="cc_icon ic_ae">American Express</span>
+        <span class="cc_icon ic_disc">Discover</span>
+      </div>
+    </div>
+    <div class="cc_row cc_num">
+      <label for="cardnum">Card #:</label>
+      <input type="text" name="cardnum" id="cardnum" maxlength="19" class="check_text">
+    </div>
+    <div class="cc_row">
+      <label for="expdate">Expire Date:</label>
+      <input type="text" name="expdate" id="expdate" maxlength="5" class="check_text">
+      <span>MM/YY</span>
+    </div>
+    <div class="cc_row">
+      <label for="cvv2">CCV2:</label>
+      <input type="text" name="cvv2" id="cvv2" maxlength="4" class="check_text">
+      <a href="https://www.runningwarehouse.com/cvv2.html#cvv2_info" class="lightboxpop" data-boxheight="375" data-boxwidth="500">what's this?</a>
+    </div>
+  </div>
+</div>