Restrict JavaScript dialogs to 100 characters.

components/app_modal/javascript_dialog_manager.cc

Index: components/app_modal/javascript_dialog_manager.cc
diff --git a/components/app_modal/javascript_dialog_manager.cc b/components/app_modal/javascript_dialog_manager.cc
index 7c4db07af63ab2e967dcdb9e2dbb2dd659e6a4d5..97d9582b6ac09a8d5f766727cab6f77d631df0ff 100644
--- a/components/app_modal/javascript_dialog_manager.cc
+++ b/components/app_modal/javascript_dialog_manager.cc
@@ -24,6 +24,7 @@
 #include "net/base/net_util.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/gfx/font_list.h"
+#include "ui/gfx/text_elider.h"
 
 namespace app_modal {
 namespace {
@@ -57,6 +58,12 @@ bool ShouldDisplaySuppressCheckbox(
   return extra_data->has_already_shown_a_dialog_;
 }
 
+// JavaScript dialogs are heavily used for scams; reduce their power by removing
+// their ability to show long messages.
+base::string16 TruncateMessage(const base::string16& message) {
+  return gfx::TruncateString(message, 100, gfx::CHARACTER_BREAK);

[Peter Kasting, 2016/02/19 02:18:34]

Please use an eliding method rather than a truncation method so that at least
the message looks like we've elided it instead of just looking like a bug.

[Avi (use Gerrit), 2016/02/19 02:24:42]

This was a bad implementation; doing it in a new way in the new patchset.

+}
+
 }  // namespace
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -153,7 +160,7 @@ void JavaScriptDialogManager::RunJavaScriptDialog(
       &javascript_dialog_extra_data_,
       dialog_title,
       message_type,
-      message_text,
+      TruncateMessage(message_text),
       default_prompt_text,
       ShouldDisplaySuppressCheckbox(extra_data),
       false,  // is_before_unload_dialog
@@ -184,8 +191,8 @@ void JavaScriptDialogManager::RunBeforeUnloadDialog(
   const base::string16 footer = l10n_util::GetStringUTF16(is_reload ?
       IDS_BEFORERELOAD_MESSAGEBOX_FOOTER : IDS_BEFOREUNLOAD_MESSAGEBOX_FOOTER);
 
-  base::string16 full_message =
-      message_text + base::ASCIIToUTF16("\n\n") + footer;
+  base::string16 message =
+      TruncateMessage(message_text) + base::ASCIIToUTF16("\n\n") + footer;
 
   extensions_client_->OnDialogOpened(web_contents);
 
@@ -194,7 +201,7 @@ void JavaScriptDialogManager::RunBeforeUnloadDialog(
       &javascript_dialog_extra_data_,
       title,
       content::JAVASCRIPT_MESSAGE_TYPE_CONFIRM,
-      full_message,
+      message,
       base::string16(),  // default_prompt_text
       ShouldDisplaySuppressCheckbox(extra_data),
       true,        // is_before_unload_dialog