[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..2d9b65b99f10274992da21b9ca998af2faf2ad65 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);
     }
   }
 
@@ -328,7 +330,20 @@ BOOL SwizzleNSExceptionInit() {
         [NSString stringWithFormat:@"%@ tag %d sending %@ to %p",
                   [sender className], tag, actionString, aTarget];
 
+  // 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:)) {
+    enableNSExceptions = true;
+  }
+
+  // These should be as close to the super call as reasonable.
+  base::mac::ScopedNSExceptionEnabler enabler(enableNSExceptions);
   ScopedCrashKey key(kActionKey, value);

[Mark Mentovai, 2011/05/17 22:23:27]

Can’t this precede ScopedNSExceptionEnabler? You can still put it after the
logic that sets enableNSExceptions. (And you can still put the logic that sets
enableNSExceptions above the thing that figures out actionString and value, so
that those can stay right next to the ScopedCrashKey for kActionKey.)

[Scott Hess - ex-Googler, 2011/05/17 22:48:30]

I'm not entirely sure I understand what you'd like to see.  One has to come
first, one has to come second, but they can generally be in any old order and
the additional exposure of one order versus the other is pretty minimal.  The
reason I pulled setting |enableNSExceptions| down by using it was just because
it seemed like keeping the new code all together was somewhat valuable.

I'll grant a slight win to not allowing exceptions while setting a
ScopedCrashKey.

+
   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, the flag must be reset so that
+    // future exceptions are not masked.

[Mark Mentovai, 2011/05/17 22:23:27]

Can you at least say here that stuff will have unwound past the outermost
ScopedNSExceptionEnabler?

[Scott Hess - ex-Googler, 2011/05/17 22:48:30]

OK.

+    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