Clean CookieSettings dependencies for componentization.

This CL prepares CookieSettings for componentization, so that it can be
shared with the iOS platform.

The detailed changes are:
- the extension scheme is injected through the constructor,
- the kBlockThirdPartyCookies preference is componentized,
- threads checks with ThreadChecker instead of BrowserThread,
- metrics are moved to the factory.

Note that the CookieSettings factory is not going to be componentized.
Follow up CLs will split the factory in a separate file and move
CookieSettings to //components/content_settings/core/browser.

BUG=503973
TBR=jochen

Review URL: https://codereview.chromium.org/1219433002

Cr-Commit-Position: refs/heads/master@{#336383}

2 files changed, 5 insertions, 0 deletions

diff --git a/components/content_settings/core/common/pref_names.cc b/components/content_settings/core/common/pref_names.cc
index c8de238..ac31d79 100644
--- a/components/content_settings/core/common/pref_names.cc
+++ b/components/content_settings/core/common/pref_names.cc
@@ -6,6 +6,10 @@
 
 namespace prefs {
 
+// Boolean that is true if we should unconditionally block third-party cookies,
+// regardless of other content settings.
+const char kBlockThirdPartyCookies[] = "profile.block_third_party_cookies";
+
 // Version of the pattern format used to define content settings.
 const char kContentSettingsVersion[] = "profile.content_settings.pref_version";
 
diff --git a/components/content_settings/core/common/pref_names.h b/components/content_settings/core/common/pref_names.h
index 3ee44b2..fabce57 100644
--- a/components/content_settings/core/common/pref_names.h
+++ b/components/content_settings/core/common/pref_names.h
@@ -9,6 +9,7 @@
 
 namespace prefs {
 
+extern const char kBlockThirdPartyCookies[];
 extern const char kContentSettingsVersion[];
 extern const char kContentSettingsPatternPairs[];
 extern const char kContentSettingsWindowLastTabIndex[];