Enable iPad Tab Switcher by default on iOS.

ios/chrome/browser/snapshots/snapshot_cache.mm

Index: ios/chrome/browser/snapshots/snapshot_cache.mm
diff --git a/ios/chrome/browser/snapshots/snapshot_cache.mm b/ios/chrome/browser/snapshots/snapshot_cache.mm
index 7da1d618c584e5c2630faf08c3f14c384596dcc4..3302036916768effc2719c2a05bf75a91de54442 100644
--- a/ios/chrome/browser/snapshots/snapshot_cache.mm
+++ b/ios/chrome/browser/snapshots/snapshot_cache.mm
@@ -27,6 +27,11 @@
 + (base::FilePath)greyImagePathForSessionID:(NSString*)sessionID;
 // Returns the directory where the thumbnails are saved.
 + (base::FilePath)cacheDirectory;
+// Returns whether the in-memory cache (as opposed to the on-disk cache) is
+// enabled.
+- (BOOL)inMemoryCacheIsEnabled;
+// Returns whether the snapshots are cached in a LRU cache.
+- (BOOL)useLRUCache;
 // Returns the directory where the thumbnails were stored in M28 and earlier.
 - (base::FilePath)oldCacheDirectory;
 // Remove all UIImages from |imageDictionary_|.
@@ -144,52 +149,45 @@ void ConvertAndSaveGreyImage(
     DCHECK_CURRENTLY_ON_WEB_THREAD(web::WebThread::UI);
     propertyReleaser_SnapshotCache_.Init(self, [SnapshotCache class]);
 
-    // Always use the LRUCache when the tab switcher is enabled.
-    if (experimental_flags::IsTabSwitcherEnabled() ||
-        experimental_flags::IsLRUSnapshotCacheEnabled()) {
+    if ([self useLRUCache]) {
       lruCache_.reset(
           [[LRUCache alloc] initWithCacheSize:kLRUCacheMaxCapacity]);
     } else {
       imageDictionary_.reset(
           [[NSMutableDictionary alloc] initWithCapacity:kCacheInitialCapacity]);
     }
-
-    if (!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled()) {
-      [[NSNotificationCenter defaultCenter]
-          addObserver:self
-             selector:@selector(handleLowMemory)
-                 name:UIApplicationDidReceiveMemoryWarningNotification
-               object:nil];
-      [[NSNotificationCenter defaultCenter]
-          addObserver:self
-             selector:@selector(handleEnterBackground)
-                 name:UIApplicationDidEnterBackgroundNotification
-               object:nil];
-      [[NSNotificationCenter defaultCenter]
-          addObserver:self
-             selector:@selector(handleBecomeActive)
-                 name:UIApplicationDidBecomeActiveNotification
-               object:nil];
-    }
+    [[NSNotificationCenter defaultCenter]
+        addObserver:self
+           selector:@selector(handleLowMemory)
+               name:UIApplicationDidReceiveMemoryWarningNotification
+             object:nil];
+    [[NSNotificationCenter defaultCenter]
+        addObserver:self
+           selector:@selector(handleEnterBackground)
+               name:UIApplicationDidEnterBackgroundNotification
+             object:nil];
+    [[NSNotificationCenter defaultCenter]
+        addObserver:self
+           selector:@selector(handleBecomeActive)
+               name:UIApplicationDidBecomeActiveNotification
+             object:nil];
   }
   return self;
 }
 
 - (void)dealloc {
-  if (!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled()) {
-    [[NSNotificationCenter defaultCenter]
-        removeObserver:self
-                  name:UIApplicationDidReceiveMemoryWarningNotification
-                object:nil];
-    [[NSNotificationCenter defaultCenter]
-        removeObserver:self
-                  name:UIApplicationDidEnterBackgroundNotification
-                object:nil];
-    [[NSNotificationCenter defaultCenter]
-        removeObserver:self
-                  name:UIApplicationDidBecomeActiveNotification
-                object:nil];
-  }
+  [[NSNotificationCenter defaultCenter]
+      removeObserver:self
+                name:UIApplicationDidReceiveMemoryWarningNotification
+              object:nil];
+  [[NSNotificationCenter defaultCenter]
+      removeObserver:self
+                name:UIApplicationDidEnterBackgroundNotification
+              object:nil];
+  [[NSNotificationCenter defaultCenter]
+      removeObserver:self
+                name:UIApplicationDidBecomeActiveNotification
+              object:nil];
   [super dealloc];
 }
 
@@ -210,9 +208,7 @@ void ConvertAndSaveGreyImage(
   DCHECK_CURRENTLY_ON_WEB_THREAD(web::WebThread::UI);
   DCHECK(sessionID);
 
-  // Cache on iPad is enabled only when the tab switcher is enabled.
-  if ((IsIPadIdiom() && !experimental_flags::IsTabSwitcherEnabled()) &&
-      !callback)
+  if (![self inMemoryCacheIsEnabled] && !callback)
     return;
 
   UIImage* img = nil;
@@ -236,9 +232,7 @@ void ConvertAndSaveGreyImage(
             [SnapshotCache imagePathForSessionID:sessionID]) retain]);
       }),
       base::BindBlock(^(base::scoped_nsobject<UIImage> image) {
-        // Cache on iPad is enabled only when the tab switcher is enabled.
-        if ((!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled()) &&
-            image) {
+        if ([self inMemoryCacheIsEnabled] && image) {
           if (lruCache_)
             [lruCache_ setObject:image forKey:sessionID];
           else
@@ -254,8 +248,7 @@ void ConvertAndSaveGreyImage(
   if (!img || !sessionID)
     return;
 
-  // Cache on iPad is enabled only when the tab switcher is enabled.
-  if (!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled()) {
+  if ([self inMemoryCacheIsEnabled]) {
     if (lruCache_)
       [lruCache_ setObject:img forKey:sessionID];
     else
@@ -386,8 +379,18 @@ void ConvertAndSaveGreyImage(
   }
 }
 
+- (BOOL)inMemoryCacheIsEnabled {
+  // In-memory cache on iPad is enabled only when the tab switcher is enabled.
+  return !IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled();
+}
+
+- (BOOL)useLRUCache {
+  // Always use the LRUCache when the tab switcher is enabled.
+  return experimental_flags::IsTabSwitcherEnabled() ||
+         experimental_flags::IsLRUSnapshotCacheEnabled();
+}
+
 - (void)handleLowMemory {
-  DCHECK(!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled());
   DCHECK_CURRENTLY_ON_WEB_THREAD(web::WebThread::UI);
   NSMutableDictionary* dictionary =
       [[NSMutableDictionary alloc] initWithCapacity:2];
@@ -410,14 +413,12 @@ void ConvertAndSaveGreyImage(
 }
 
 - (void)handleEnterBackground {
-  DCHECK(!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled());
   DCHECK_CURRENTLY_ON_WEB_THREAD(web::WebThread::UI);
   [imageDictionary_ removeAllObjects];
   [lruCache_ removeAllObjects];
 }
 
 - (void)handleBecomeActive {
-  DCHECK(!IsIPadIdiom() || experimental_flags::IsTabSwitcherEnabled());
   DCHECK_CURRENTLY_ON_WEB_THREAD(web::WebThread::UI);
   for (NSString* sessionID in pinnedIDs_)
     [self retrieveImageForSessionID:sessionID callback:nil];
@@ -568,11 +569,12 @@ void ConvertAndSaveGreyImage(
 @implementation SnapshotCache (TestingAdditions)
 
 - (BOOL)hasImageInMemory:(NSString*)sessionID {
-  if (experimental_flags::IsLRUSnapshotCacheEnabled())
+  if ([self useLRUCache])
     return [lruCache_ objectForKey:sessionID] != nil;
   else
     return [imageDictionary_ objectForKey:sessionID] != nil;
 }
+
 - (BOOL)hasGreyImageInMemory:(NSString*)sessionID {
   return [greyImageDictionary_ objectForKey:sessionID] != nil;
 }