Make session restore understand that tabs have multiple SessionStorageNamespaces.

content/browser/browser_context.cc

Index: content/browser/browser_context.cc
diff --git a/content/browser/browser_context.cc b/content/browser/browser_context.cc
index d1e481c5aa48762bb7e56b196564c9410ce97909..ec9982134c4334116a9f84d80811272d2dbbcb58 100644
--- a/content/browser/browser_context.cc
+++ b/content/browser/browser_context.cc
@@ -211,6 +211,13 @@ fileapi::FileSystemContext* BrowserContext::GetFileSystemContext(
   return partition->filesystem_context();
 }
 
+bool BrowserContext::IsValidStoragePartitionId(
+    BrowserContext* browser_context,
+    const std::string& partition_id) {
+  return GetContentClient()->browser()->IsValidStoragePartitionId(
+      browser_context, partition_id);
+}
+
 void BrowserContext::EnsureResourceContextInitialized(BrowserContext* context) {
   // This will be enough to tickle initialization of BrowserContext if
   // necessary, which initializes ResourceContext. The reason we don't call