Added an experiment for an LRU snapshot cache.

ios/chrome/browser/snapshots/snapshot_cache_unittest.mm

Index: ios/chrome/browser/snapshots/snapshot_cache_unittest.mm
diff --git a/ios/chrome/browser/snapshots/snapshot_cache_unittest.mm b/ios/chrome/browser/snapshots/snapshot_cache_unittest.mm
index c77a9ae94f56d7d2b24d2c93758101c6001a9901..42b45cad54ce113cedf4d623ee5f639a8ae5e025 100644
--- a/ios/chrome/browser/snapshots/snapshot_cache_unittest.mm
+++ b/ios/chrome/browser/snapshots/snapshot_cache_unittest.mm
@@ -16,6 +16,7 @@
 #include "base/run_loop.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/time/time.h"
+#include "ios/chrome/browser/experimental_flags.h"
 #include "ios/chrome/browser/ui/ui_util.h"
 #include "ios/web/public/test/test_web_thread_bundle.h"
 #include "ios/web/public/web_thread.h"
@@ -40,11 +41,19 @@ static const NSUInteger kSnapshotPixelSize = 8;
 
 @implementation SnapshotCache (TestingAdditions)

[sdefresne, 2015/11/03 11:25:19]

Please avoid adding methods to the class in the test file. Can you move this to
a private part of the SnapshotCache class?

[jbbegue, 2015/11/03 13:37:19]

Done.

 - (BOOL)hasImageInMemory:(NSString*)sessionID {
-  return [imageDictionary_ objectForKey:sessionID] != nil;
+  if (experimental_flags::IsLRUSnapshotCacheEnabled())
+    return [lruCache_ objectForKey:sessionID] != nil;
+  else
+    return [imageDictionary_ objectForKey:sessionID] != nil;
 }
 - (BOOL)hasGreyImageInMemory:(NSString*)sessionID {
   return [greyImageDictionary_ objectForKey:sessionID] != nil;
 }
+
+- (NSUInteger)lruCacheMaxSize {
+  return [lruCache_ maxCacheSize];
+}
+
 @end
 
 namespace {
@@ -235,8 +244,12 @@ TEST_F(SnapshotCacheTest, Cache) {
 
   SnapshotCache* cache = GetSnapshotCache();
 
+  NSUInteger expectedCacheSize = kSessionCount;
+  if (experimental_flags::IsLRUSnapshotCacheEnabled())
+    expectedCacheSize = MIN(kSessionCount, [cache lruCacheMaxSize]);
+
   // Put all images in the cache.
-  for (NSUInteger i = 0; i < kSessionCount; ++i) {
+  for (NSUInteger i = 0; i < expectedCacheSize; ++i) {
     UIImage* image = [testImages_ objectAtIndex:i];
     NSString* sessionID = [testSessions_ objectAtIndex:i];
     [cache setImage:image withSessionID:sessionID];
@@ -244,7 +257,7 @@ TEST_F(SnapshotCacheTest, Cache) {
 
   // Get images back.
   __block NSUInteger numberOfCallbacks = 0;
-  for (NSUInteger i = 0; i < kSessionCount; ++i) {
+  for (NSUInteger i = 0; i < expectedCacheSize; ++i) {
     NSString* sessionID = [testSessions_ objectAtIndex:i];
     UIImage* expectedImage = [testImages_ objectAtIndex:i];
     EXPECT_TRUE(expectedImage != nil);
@@ -256,7 +269,7 @@ TEST_F(SnapshotCacheTest, Cache) {
                               ++numberOfCallbacks;
                             }];
   }
-  EXPECT_EQ(kSessionCount, numberOfCallbacks);
+  EXPECT_EQ(MIN(expectedCacheSize, [cache lruCacheMaxSize]), numberOfCallbacks);
 }
 
 // This test puts all the snapshots in the cache and flushes them to disk.