Use base::StringPairs where appropriate from /chrome

Becuase base/strings/string_split.h defines:
typedef std::vector<std::pair<std::string, std::string> > StringPairs;

BUG=412250

Review URL: https://codereview.chromium.org/568173004

Cr-Commit-Position: refs/heads/master@{#294707}

chrome/browser/chromeos/drive/resource_metadata_storage_unittest.cc

@@ -8,6 +8,7 @@
 
 #include "base/files/file_util.h"
 #include "base/files/scoped_temp_dir.h"
+#include "base/strings/string_split.h"
 #include "chrome/browser/chromeos/drive/drive.pb.h"
 #include "chrome/browser/chromeos/drive/test_util.h"
 #include "content/public/test/test_browser_thread_bundle.h"
@@ -198,8 +199,7 @@ TEST_F(ResourceMetadataStorageTest, GetIdByResourceId) {
 TEST_F(ResourceMetadataStorageTest, GetChildren) {
   const std::string parents_id[] = { "mercury", "venus", "mars", "jupiter",
                                      "saturn" };
-  std::vector<std::vector<std::pair<std::string, std::string> > >
-      children_name_id(arraysize(parents_id));
+  std::vector<base::StringPairs> children_name_id(arraysize(parents_id));
   // Skip children_name_id[0/1] here because Mercury and Venus have no moon.
   children_name_id[2].push_back(std::make_pair("phobos", "mars_i"));
   children_name_id[2].push_back(std::make_pair("deimos", "mars_ii"));

chrome/browser/content_settings/content_settings_pref_provider.cc

@@ -14,6 +14,7 @@
 #include "base/metrics/histogram.h"
 #include "base/prefs/pref_service.h"
 #include "base/prefs/scoped_user_pref_update.h"
+#include "base/strings/string_split.h"
 #include "base/time/clock.h"
 #include "base/time/default_clock.h"
 #include "chrome/browser/content_settings/content_settings_rule.h"
@@ -509,7 +510,7 @@ void PrefProvider::CanonicalizeContentSettingsExceptions(
   DCHECK(all_settings_dictionary);
 
   std::vector<std::string> remove_items;
-  std::vector<std::pair<std::string, std::string> > move_items;
+  base::StringPairs move_items;
   for (base::DictionaryValue::Iterator i(*all_settings_dictionary);
        !i.IsAtEnd();
        i.Advance()) {

chrome/browser/extensions/api/identity/gaia_web_auth_flow.cc

@@ -165,7 +165,7 @@ void GaiaWebAuthFlow::OnAuthFlowURLChange(const GURL& url) {
 
     std::string fragment = url.GetContent().substr(
         redirect_path_prefix_.length(), std::string::npos);
-    std::vector<std::pair<std::string, std::string> > pairs;
+    base::StringPairs pairs;
     base::SplitStringIntoKeyValuePairs(fragment, '=', '&', &pairs);
     std::string access_token;
     std::string error;

chrome/browser/prefs/tracked/tracked_preferences_migration_unittest.cc

@@ -12,6 +12,7 @@
 #include "base/callback.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/prefs/testing_pref_service.h"
+#include "base/strings/string_split.h"
 #include "base/values.h"
 #include "chrome/browser/prefs/interceptable_pref_filter.h"
 #include "chrome/browser/prefs/pref_hash_store.h"
@@ -219,8 +220,7 @@ class TrackedPreferencesMigrationTest : public testing::Test {
   // in the store identified by |store_id|.
   void VerifyValuesStored(
       MockPrefStoreID store_id,
-      const std::vector<std::pair<std::string, std::string> >&
-          expected_prefs_in_store) {
+      const base::StringPairs& expected_prefs_in_store) {
     base::DictionaryValue* store = NULL;
     switch (store_id) {
       case MOCK_UNPROTECTED_PREF_STORE:
@@ -232,8 +232,7 @@ class TrackedPreferencesMigrationTest : public testing::Test {
     }
     DCHECK(store);
 
-    for (std::vector<std::pair<std::string, std::string> >::const_iterator it =
-             expected_prefs_in_store.begin();
+    for (base::StringPairs::const_iterator it = expected_prefs_in_store.begin();
          it != expected_prefs_in_store.end(); ++it) {
       std::string val;
       EXPECT_TRUE(store->GetString(it->first, &val));
@@ -474,12 +473,12 @@ TEST_F(TrackedPreferencesMigrationTest, NoMigrationRequired) {
   EXPECT_FALSE(StoreModifiedByMigration(MOCK_UNPROTECTED_PREF_STORE));
   EXPECT_FALSE(StoreModifiedByMigration(MOCK_PROTECTED_PREF_STORE));
 
-  std::vector<std::pair<std::string, std::string> > expected_unprotected_values;
+  base::StringPairs expected_unprotected_values;
   expected_unprotected_values.push_back(
       std::make_pair(kUnprotectedPref, kUnprotectedPrefValue));
   VerifyValuesStored(MOCK_UNPROTECTED_PREF_STORE, expected_unprotected_values);
 
-  std::vector<std::pair<std::string, std::string> > expected_protected_values;
+  base::StringPairs expected_protected_values;
   expected_protected_values.push_back(
       std::make_pair(kProtectedPref, kProtectedPrefValue));
   VerifyValuesStored(MOCK_PROTECTED_PREF_STORE, expected_protected_values);

chrome/browser/ui/webui/net_internals/net_internals_ui.cc

@@ -1211,7 +1211,7 @@ void NetInternalsMessageHandler::IOThreadImpl::OnGetHttpCacheInfo(
 
   if (disk_cache) {
     // Extract the statistics key/value pairs from the backend.
-    std::vector<std::pair<std::string, std::string> > stats;
+    base::StringPairs stats;
     disk_cache->GetStats(&stats);
     for (size_t i = 0; i < stats.size(); ++i) {
       stats_dict->SetStringWithoutPathExpansion(