Plumb through cache_identity from manifest for first sketch of pnacl cache.

ppapi/native_client/src/trusted/plugin/manifest.h

Index: ppapi/native_client/src/trusted/plugin/manifest.h
diff --git a/ppapi/native_client/src/trusted/plugin/manifest.h b/ppapi/native_client/src/trusted/plugin/manifest.h
index 18aed651faea17be26b62540fed7e447f368ec98..bce0a19091f72555ef6b73e6149c1993ab593b84 100644
--- a/ppapi/native_client/src/trusted/plugin/manifest.h
+++ b/ppapi/native_client/src/trusted/plugin/manifest.h
@@ -41,6 +41,7 @@ class Manifest {
   // manifest file. Sets |pnacl_translate| to |true| if the program is
   // requires pnacl translation.
   virtual bool GetProgramURL(nacl::string* full_url,
+                             nacl::string* cache_identity,
                              ErrorInfo* error_info,
                              bool* pnacl_translate) const = 0;
 
@@ -62,6 +63,7 @@ class Manifest {
   // If there was an error, details are reported via error_info.
   virtual bool ResolveKey(const nacl::string& key,
                           nacl::string* full_url,
+                          nacl::string* cache_identity,
                           ErrorInfo* error_info,
                           bool* pnacl_translate) const = 0;