Migrate TabPersistentStore to one shared directory for multi-instance

Rather than using a sub-directory per ChromeTabbedActivity instance,
use one shared director for all instances.

BUG=622143

Review-Url: https://codereview.chromium.org/2087893003
Cr-Commit-Position: refs/heads/master@{#403229}
diff --git a/chrome/android/java_sources.gni b/chrome/android/java_sources.gni
index 746068d..89760131 100644
--- a/chrome/android/java_sources.gni
+++ b/chrome/android/java_sources.gni
@@ -1214,6 +1214,7 @@
   "javatests/src/org/chromium/chrome/browser/tabmodel/ChromeTabCreatorTest.java",
   "javatests/src/org/chromium/chrome/browser/tabmodel/ContextMenuLoadUrlParamsTest.java",
   "javatests/src/org/chromium/chrome/browser/tabmodel/DocumentModeAssassinTest.java",
+  "javatests/src/org/chromium/chrome/browser/tabmodel/MultiInstanceMigrationTest.java",
   "javatests/src/org/chromium/chrome/browser/tabmodel/OffTheRecordTabModelTest.java",
   "javatests/src/org/chromium/chrome/browser/tabmodel/RestoreMigrateTest.java",
   "javatests/src/org/chromium/chrome/browser/tabmodel/TabModelSelectorTabObserverTest.java",