Issue mozilla-mobile#11300: EngineMiddleware: Add option for disabling TrimMemoryMiddleware

Author: pocmo

components/browser/state/src/main/java/mozilla/components/browser/state/engine/EngineMiddleware.kt

@@ -28,10 +28,14 @@ object EngineMiddleware {
     /**
      * Creates a list of [Middleware] to be installed on a [BrowserStore] in order to support all
      * [EngineAction]s.
+     *
+     * @param trimMemoryAutomatically Whether a middleware should listen to LowMemoryAction and
+     * automatically trim memory by suspending tabs.
      */
     fun create(
         engine: Engine,
-        scope: CoroutineScope = MainScope()
+        scope: CoroutineScope = MainScope(),
+        trimMemoryAutomatically: Boolean = true
     ): List<Middleware<BrowserState, BrowserAction>> {
         return listOf(
             EngineDelegateMiddleware(scope),
@@ -43,8 +47,11 @@ object EngineMiddleware {
             TabsRemovedMiddleware(scope),
             SuspendMiddleware(scope),
             WebExtensionMiddleware(),
-            TrimMemoryMiddleware(),
             CrashMiddleware()
-        )
+        ) + if (trimMemoryAutomatically) {
+            listOf(TrimMemoryMiddleware())
+        } else {
+            emptyList()
+        }
     }
 }

components/browser/state/src/test/java/mozilla/components/browser/state/engine/EngineMiddlewareTest.kt

@@ -11,6 +11,7 @@ import kotlinx.coroutines.test.TestCoroutineDispatcher
 import kotlinx.coroutines.test.resetMain
 import kotlinx.coroutines.test.setMain
 import mozilla.components.browser.state.action.EngineAction
+import mozilla.components.browser.state.engine.middleware.TrimMemoryMiddleware
 import mozilla.components.browser.state.state.BrowserState
 import mozilla.components.browser.state.state.createTab
 import mozilla.components.browser.state.store.BrowserStore
@@ -19,6 +20,7 @@ import mozilla.components.concept.engine.EngineSession
 import mozilla.components.support.test.libstate.ext.waitUntilIdle
 import mozilla.components.support.test.mock
 import org.junit.After
+import org.junit.Assert.assertTrue
 import org.junit.Before
 import org.junit.Test
 import org.mockito.Mockito
@@ -72,4 +74,23 @@ class EngineMiddlewareTest {
 
         verify(engine, Mockito.times(1)).createSession(false, null)
     }
+
+    @Test
+    fun `TrimMemoryMiddleware will be added by default`() {
+        val list = EngineMiddleware.create(
+            engine = mock()
+        )
+
+        assertTrue(list.any { it is TrimMemoryMiddleware })
+    }
+
+    @Test
+    fun `TrimMemoryMiddleware will not be added if trimMemoryAutomatically is set to false`() {
+        val list = EngineMiddleware.create(
+            engine = mock(),
+            trimMemoryAutomatically = false
+        )
+
+        assertTrue(list.none { it is TrimMemoryMiddleware })
+    }
 }