Truncate the Javascript alert message if the length is too long on Mac port

chrome/browser/ui/cocoa/javascript_app_modal_dialog_cocoa.mm

Index: chrome/browser/ui/cocoa/javascript_app_modal_dialog_cocoa.mm
diff --git a/chrome/browser/ui/cocoa/javascript_app_modal_dialog_cocoa.mm b/chrome/browser/ui/cocoa/javascript_app_modal_dialog_cocoa.mm
index 7341835b372e3527306b29bcf4a07474317b3d93..f98b7d39974368f3600a3c354bdb459db06a2e12 100644
--- a/chrome/browser/ui/cocoa/javascript_app_modal_dialog_cocoa.mm
+++ b/chrome/browser/ui/cocoa/javascript_app_modal_dialog_cocoa.mm
@@ -17,6 +17,9 @@
 #include "ui/base/l10n/l10n_util_mac.h"
 #include "ui/base/ui_base_types.h"
 
+const int kSlotsPerLine = 50;
+const int kMessageTextMaxSlots = 2000;
+
 // Helper object that receives the notification that the dialog/sheet is
 // going away. Is responsible for cleaning itself up.
 @interface JavaScriptAppModalDialogHelper : NSObject<NSAlertDelegate> {
@@ -146,6 +149,23 @@ JavaScriptAppModalDialogCocoa::JavaScriptAppModalDialogCocoa(
   [alert_ setDelegate:helper_];
   NSString* informative_text =
       base::SysUTF16ToNSString(dialog_->message_text());
+
+  // Truncate long JS alerts - crbug.com/331219
+  NSCharacterSet* newline_char_set = [NSCharacterSet newlineCharacterSet];
+  for (size_t index = 0, slots_count = 0; index < informative_text.length;
+      ++index) {
+    unichar current_char = [informative_text characterAtIndex:index];
+    if ([newline_char_set characterIsMember:current_char])
+      slots_count += kSlotsPerLine;
+    else
+      slots_count++;
+    if (slots_count > kMessageTextMaxSlots) {
+      informative_text = [informative_text substringToIndex:index - 1];

[Avi (use Gerrit), 2014/01/24 20:08:08]

But that's what you're doing here with -substringToIndex:! It, as well as
TruncateString, takes a length to truncate to. You could easily put in
TruncateString here with i as the length.

+      informative_text = [informative_text stringByAppendingString:@"\n..."];
+      break;
+    }
+  }
+
   [alert_ setInformativeText:informative_text];
   NSString* message_text =
       base::SysUTF16ToNSString(dialog_->title());