[ObjC ARC] Converts ios/web:web to ARC.

ios/web/public/test/web_test.h

Index: ios/web/public/test/web_test.h
diff --git a/ios/web/public/test/web_test.h b/ios/web/public/test/web_test.h
index 27002abd4f36efc9ef409a3fcb913d44c22ed53c..c6993c33e13546d8d536634bd48c990c6c358753 100644
--- a/ios/web/public/test/web_test.h
+++ b/ios/web/public/test/web_test.h
@@ -49,6 +49,16 @@ class WebTest : public PlatformTest {
 
   // Triggers test failures if a render process dies during the test.
   std::unique_ptr<WebTestRenderProcessCrashObserver> crash_observer_;
+
+  // The system autorelease pool is deallocated after some of the C++ objects
+  // have been destroyed in the test (e.g. WebThreadImpl). Therefore any
+  // autoreleased object will be deallocated after a lot of the expected
+  // application context is gone, causing DCHECKs on deallocation. Creating our
+  // own root pool wrapping the test ensures that autoreleased objects are
+  // released at the end of the test, not later after the C++ test objects are
+  // destroyed.
+  // Of type ID to prevent ARC imports from complaining about NSAutoreleasePool.
+  id root_pool_;

[Eugene But (OOO till 7-30), 2017/06/12 06:12:51]

Using |id| makes this header an Objective-C header so now it has to be imported
everywhere, instead of included.

[stkhapugin, 2017/06/12 12:36:23]

Please don't create a bare objc pointer in a header. Instead, do one of the
following:

1. This header is included only from ARC files. Then mark this as
__strong/__weak explicitly. In case of __strong, add a compilation guard to the
header, too. 
2. This header is included from both ARC and non-ARC. Then:
  a) This is a strong -> make it scoped_nsobject
  b) This is a weak -> make it __unsafe_unretained with a comment //weak to
change it to __weak once all the including files are built with ARC
  c) This actually needs to be a zeroing weak - use WeakNSObject

[PL, 2017/06/14 00:31:10]

Thanks both, this is great guidance.

In the next revision I've actually changed this significantly removing this
altogether, because:

• web_test.mm is now ARC so can't use NSAutoreleasePool at all, and @autorelease
can't span methods.
• We still have a fundamental problem with some test objects being captured by
an autorelease pool that's released after all the C++ objects are destroyed.
• One alternative is to have a new superclass that never becomes ARCified, and
that wraps SetUp and TearDown in an autorelease pool. But this feels very heavy.
• My proposed solution (in the revision) uses ARC autoreleasepool blocks
instead, although it's needed in three places. I recommend that we do this, and
file a bug on the gtest team(?) to have SetUp and TearDown to have its own pool
(the Mac PlatformTest class already has a pool wrapping an entire test suite, so
doesn't seem a stretch to add one per test).

 };
 
 }  // namespace web