Bug 1580212, part 2 - Make dom.ipc.keepProcessesAlive.webIsolated work for Fission content processes. r=kmag

Also, enable it for the extensions test directory. Without this pref,
it gets frequent intermittent leaks and shutdown hangs when Fission is
enabled.

Differential Revision: https://phabricator.services.mozilla.com/D51752

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

browser/components/extensions/test/browser/browser.ini

@@ -4,6 +4,10 @@ prefs =
     # We don't want to reset this at the end of the test, so that we don't have
     # to spawn a new extension child process for each test unit.
     dom.ipc.keepProcessesAlive.extension=1
+    # With Fission enabled, this directory spawns many child processes, which
+    # somehow results in frequent leaks and shutdown hangs. Reuse the content
+    # processes to avoid this.
+    dom.ipc.keepProcessesAlive.webIsolated.perOrigin=1
     dom.animations-api.core.enabled=true
     dom.animations-api.timelines.enabled=true
     plugin.load_flash_only=false

dom/ipc/ContentParent.cpp

@@ -232,6 +232,7 @@
 #include "MMPrinter.h"
 #include "nsStreamUtils.h"
 #include "nsIAsyncInputStream.h"
+#include "xpcpublic.h"
 
 #include "mozilla/Sprintf.h"
 
@@ -1809,7 +1810,15 @@ bool ContentParent::ShouldKeepProcessAlive() {
   int32_t processesToKeepAlive = 0;
 
   nsAutoCString keepAlivePref("dom.ipc.keepProcessesAlive.");
-  keepAlivePref.Append(NS_ConvertUTF16toUTF8(mRemoteType));
+
+  if (StringBeginsWith(mRemoteType,
+                       NS_LITERAL_STRING(FISSION_WEB_REMOTE_TYPE)) &&
+      xpc::IsInAutomation()) {
+    keepAlivePref.Append(FISSION_WEB_REMOTE_TYPE);
+    keepAlivePref.AppendLiteral(".perOrigin");
+  } else {
+    keepAlivePref.Append(NS_ConvertUTF16toUTF8(mRemoteType));
+  }
   if (NS_FAILED(
           Preferences::GetInt(keepAlivePref.get(), &processesToKeepAlive))) {
     return false;