firebase-ios-sdk

Merging the 6.8.0 release into master (#3783)

* Update versions for Release 6.8.0

* RemoteConfig fix pod spec lint (#3715) (#3716)

* ABTesting: add protos to private headers.

* RemoteConfig: #import <FirebaseABTesting/ExperimentPayload.pbobjc.h>

* ./scripts/style.sh

* Remote Config `pod spec lint` fixes (#3717) (#3718)

* Fix ExperimentPayload.pbobjc.h imports

* RemoteConfig tests: add missing headers to spec.

* Revert ExperimentPayload.pbobjc.h import for ABTesting sources.

* Add FDL to M55 (#3724)

* Remove references to UIWebView from DynamicLinks to comply with Apple "ITMS-90809: Deprecated API Usage" (#3723)
* Add FDL to M55

* Fix accessing a destroyed object (#3721) (#3725)

This was caused by running under Asan with XCode 11. Apparently, previous versions of XCode cannot catch it (which is why Travis is passing, apparently).

Also:
* enable "Detect use of stack after return" option for Asan. AFAIU, it can only be enabled in the scheme. It's already enabled for unit tests, this PR additionally enables it for integration tests;
* make Asan failures fail Travis build. They were originally not considered blocking due to some sporadic failures. I haven't seen those for some time, and worst case scenario, we can revert this change.

* Cherry pick GDT changes for 6.8.0 and increment versions (#3770)

* Release 6.8.0: cherry pick of #3764 and #3766 (#3772)

* Gate access to cached instances. (#3766)

* Gate access to cached instances.

This is causing an issue in #3728. Hopefully this will fix it, but no
repro is available yet to test. There's still an underlying race
condition where a `creationBlock` could be called twice for a component
that is supposed to cache the instance returned, but that should be
addressed in a follow up PR.

* Review feedback.

* Iterate from array copy in `latestExperimentStartTimestampBetweenTimestamp:` (#3764)

* Release 6.8.0 cherry pick: conflicting Dynamic Links changelog changes. (#3790)

* Update FDL CHANGELOG (#3781)

* Issue number, not PR number (#3785)