[Mac] Allow NSExceptions in certain cases.

chrome/browser/chrome_browser_application_mac.mm

Index: chrome/browser/chrome_browser_application_mac.mm
diff --git a/chrome/browser/chrome_browser_application_mac.mm b/chrome/browser/chrome_browser_application_mac.mm
index 745e0ab4dbb9396913f4db9a7f0da5232da12271..8760d26cc9b9361eb66d12deab07afd06f8cd10f 100644
--- a/chrome/browser/chrome_browser_application_mac.mm
+++ b/chrome/browser/chrome_browser_application_mac.mm
@@ -5,6 +5,7 @@
 #import "chrome/browser/chrome_browser_application_mac.h"
 
 #import "base/logging.h"
+#import "base/mac/scoped_nsexception_enabler.h"
 #import "base/metrics/histogram.h"
 #import "base/memory/scoped_nsobject.h"
 #import "base/sys_string_conversions.h"
@@ -93,7 +94,8 @@ static IMP gOriginalInitIMP = NULL;
     // (destructors are skipped).  Chrome should be NSException-free,
     // please check your backtrace and see if you can't file a bug
     // with a repro case.
-    if (fatal) {
+    const bool allow = base::mac::GetNSExceptionsAllowed();
+    if (fatal && !allow) {
       LOG(FATAL) << "Someone is trying to raise an exception!  "
                  << base::SysNSStringToUTF8(value);
     } else {
@@ -101,7 +103,7 @@ static IMP gOriginalInitIMP = NULL;
       // exceptions.
       DLOG(ERROR) << "Someone is trying to raise an exception!  "
                   << base::SysNSStringToUTF8(value);
-      NOTREACHED();
+      DCHECK(allow);
     }
   }
 
@@ -329,6 +331,19 @@ BOOL SwizzleNSExceptionInit() {
                   [sender className], tag, actionString, aTarget];
 
   ScopedCrashKey key(kActionKey, value);

[Mark Mentovai, 2011/05/24 00:05:16]

Yup, seeing this here, I agree that it’s fine.

+
+  // Certain third-party code, such as print drivers, can still throw
+  // exceptions and Chromium cannot fix them.  This provides a way to
+  // work around those on a spot basis.
+  bool enableNSExceptions = false;
+
+  // http://crbug.com/80686 , an Epson printer driver.
+  if (anAction == @selector(selectPDE:)) {

[Mark Mentovai, 2011/05/24 00:05:16]

If you know something about aTarget (or possibly even sender?), you can tighten
this up a bit, by calling -[aTarget isKindOfClass:[ExceptionUsingClass class]],
for example.

[Scott Hess - ex-Googler, 2011/05/24 00:31:25]

This info is from the backtrace on http://crbug.com/80686 .  class-dump'ing
around in the module list, the method is on class PMPDEController in
PrintCocoaUI.bundle in the system PrintingPrivate.framework.  So I'd likely have
to do a string comparison on the name, which is a little sketchy, but this is
far into sketchy to start with.  WTYD?

["PDE" == "Printing Dialog Extension", I'm guessing this crash happens when the
driver is prompted to load up a custom dialog and is doing something wrong.]

[Mark Mentovai, 2011/05/24 00:39:05]

shess wrote:
Blech.

Since it’s private, I’ll say “we don’t really know enough about aTarget,” so
just forget it.

+    enableNSExceptions = true;
+  }
+
+  // Minimize the window by keeping this close to the super call.
+  base::mac::ScopedNSExceptionEnabler enabler(enableNSExceptions);
   return [super sendAction:anAction to:aTarget from:sender];
 }
 
@@ -354,6 +369,11 @@ BOOL SwizzleNSExceptionInit() {
     // addressed elsewhere.
     [self clearIsHandlingSendEvent];
 
+    // If |ScopedNSExceptionEnabler| is used to allow exceptions, and an
+    // uncaught exception is thrown, it will throw past all of the scopers.
+    // Reset the flag so that future exceptions are not masked.
+    base::mac::SetNSExceptionsAllowed(false);
+
     // Store some human-readable information in breakpad keys in case
     // there is a crash.  Since breakpad does not provide infinite
     // storage, we track two exceptions.  The first exception thrown