Autofill OSX: Add RetriableErrorMessage text label.

Add error message text label between CVC input row and Verify/Cancel
buttons. Error messages passed to
CardUnmaskPromptViewBridge::GotVerificationResult() are displayed.

Dialog will re-layout to fit entire message if a multiline message is
set. Previous to this CL the layout was done exactly once per dialog,
upon dialog creation. This CL refactors the layout code out into
-performLayout and calls it whenever the error message text changes.

Screenshot attached to bug: https://code.google.com/p/chromium/issues/detail?id=448572#c14

BUG=448572

Review URL: https://codereview.chromium.org/1024553004

Cr-Commit-Position: refs/heads/master@{#322262}

chrome/browser/ui/cocoa/autofill/card_unmask_prompt_view_bridge.h

@@ -55,6 +55,7 @@ class CardUnmaskPromptViewBridge : public CardUnmaskPromptView,
 - (id)initWithBridge:(autofill::CardUnmaskPromptViewBridge*)bridge;
 
 - (void)setProgressOverlayText:(const base::string16&)text;
+- (void)setRetriableErrorMessage:(const base::string16&)text;
 
 @end