Bug 1536058 - Add Cache-Isolation behind a pref r=ckerschb,Ehsan

***

Differential Revision: https://phabricator.services.mozilla.com/D40612

--HG--
extra : moz-landing-system : lando

modules/libpref/init/StaticPrefList.yaml

@@ -645,6 +645,12 @@
   value: true
   mirror: always
 
+# Enable/Disable Origin based cache isolation
+- name: browser.cache.cache_isolation
+  type: RelaxedAtomicBool
+  value: false
+  mirror: always
+
 # -1 = determine dynamically, 0 = none, n = memory capacity in kilobytes.
 - name: browser.cache.memory.capacity
   type: RelaxedAtomicInt32

netwerk/protocol/http/nsHttpChannel.cpp

@@ -3912,9 +3912,10 @@ bool nsHttpChannel::IsIsolated() {
   if (mHasBeenIsolatedChecked) {
     return mIsIsolated;
   }
-  mIsIsolated = IsThirdPartyTrackingResource() &&
-                !AntiTrackingCommon::IsFirstPartyStorageAccessGrantedFor(
-                    this, mURI, nullptr);
+  mIsIsolated = StaticPrefs::browser_cache_cache_isolation() ||
+                (IsThirdPartyTrackingResource() &&
+                 !AntiTrackingCommon::IsFirstPartyStorageAccessGrantedFor(
+                     this, mURI, nullptr));
   mHasBeenIsolatedChecked = true;
   return mIsIsolated;
 }