[iOS] Upstream some stability code

ios/chrome/browser/metrics/previous_session_info.mm

Index: ios/chrome/browser/metrics/previous_session_info.mm
diff --git a/ios/chrome/browser/metrics/previous_session_info.mm b/ios/chrome/browser/metrics/previous_session_info.mm
new file mode 100644
index 0000000000000000000000000000000000000000..a8d0c62a54c34c7da1a89828f285817c4af3453c
--- /dev/null
+++ b/ios/chrome/browser/metrics/previous_session_info.mm
@@ -0,0 +1,106 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "ios/chrome/browser/metrics/previous_session_info.h"
+
+#include "base/logging.h"
+#include "base/mac/scoped_nsobject.h"
+#include "base/strings/sys_string_conversions.h"
+#include "ios/public/provider/chrome/browser/chrome_browser_provider.h"
+
+namespace {
+
+// Key in the UserDefaults for a boolean value keeping track of memory warnings.
+NSString* const kDidSeeMemoryWarningShortlyBeforeTerminating =
+    @"DidSeeMemoryWarning";
+
+// Key in the NSUserDefaults for a string value that stores the version of the
+// last session.
+NSString* const kLastRanVersion = @"LastRanVersion";
+
+}  // namespace
+
+@interface PreviousSessionInfo ()
+
+// Whether beginRecordingCurrentSession was called.
+@property(nonatomic, assign) BOOL didBeginRecordingCurrentSession;
+
+// Redefined to be read-write.
+@property(nonatomic, assign) BOOL didSeeMemoryWarningShortlyBeforeTerminating;
+@property(nonatomic, assign) BOOL isFirstSessionAfterUpgrade;
+
+@end
+
+@implementation PreviousSessionInfo
+
+@synthesize didBeginRecordingCurrentSession = _didBeginRecordingCurrentSession;
+@synthesize didSeeMemoryWarningShortlyBeforeTerminating =
+    _didSeeMemoryWarningShortlyBeforeTerminating;
+@synthesize isFirstSessionAfterUpgrade = _isFirstSessionAfterUpgrade;
+
+// Singleton PreviousSessionInfo.
+static PreviousSessionInfo* gSharedInstance = nil;
+
++ (instancetype)sharedInstance {
+  if (!gSharedInstance) {
+    gSharedInstance = [[PreviousSessionInfo alloc] init];
+
+    // Load the persisted information.
+    NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
+    gSharedInstance.didSeeMemoryWarningShortlyBeforeTerminating =
+        [defaults boolForKey:kDidSeeMemoryWarningShortlyBeforeTerminating];
+    NSString* lastRanVersion = [defaults stringForKey:kLastRanVersion];
+    NSString* currentVersion = base::SysUTF8ToNSString(
+        ios::GetChromeBrowserProvider()->GetVersionNumber());
+    gSharedInstance.isFirstSessionAfterUpgrade =
+        ![lastRanVersion isEqualToString:currentVersion];
+  }
+  return gSharedInstance;
+}
+
++ (void)resetSharedInstanceForTesting {
+  [gSharedInstance release];
+  gSharedInstance = nil;
+}
+
+- (void)beginRecordingCurrentSession {
+  if (self.didBeginRecordingCurrentSession)
+    return;
+  self.didBeginRecordingCurrentSession = YES;
+
+  NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
+
+  // Set the new version.
+  NSString* currentVersion = base::SysUTF8ToNSString(
+      ios::GetChromeBrowserProvider()->GetVersionNumber());
+  [defaults setObject:currentVersion forKey:kLastRanVersion];
+
+  // Clear the memory warning flag.
+  [defaults removeObjectForKey:kDidSeeMemoryWarningShortlyBeforeTerminating];
+
+  // Save critical state information for crash detection.
+  [defaults synchronize];
+}
+
+- (void)setMemoryWarningFlag {
+  if (!self.didBeginRecordingCurrentSession)
+    return;
+
+  NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
+  [defaults setBool:YES forKey:kDidSeeMemoryWarningShortlyBeforeTerminating];
+  // Save critical state information for crash detection.
+  [defaults synchronize];
+}
+
+- (void)resetMemoryWarningFlag {
+  if (!self.didBeginRecordingCurrentSession)
+    return;
+
+  NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
+  [defaults removeObjectForKey:kDidSeeMemoryWarningShortlyBeforeTerminating];
+  // Save critical state information for crash detection.
+  [defaults synchronize];
+}
+
+@end