Translate: Move label parsing logic into common code.

app/l10n_util_mac.h

Index: app/l10n_util_mac.h
diff --git a/app/l10n_util_mac.h b/app/l10n_util_mac.h
index 995d1910df3335cc379761911e26c7c4263cd0e7..6c473ac78393376a42dd7ae39a39371d69dd6999 100644
--- a/app/l10n_util_mac.h
+++ b/app/l10n_util_mac.h
@@ -42,6 +42,15 @@ NSString* GetNSStringF(int message_id,
                        const string16& c,
                        const string16& d);
 
+// Variants that return the offset(s) of the replaced parameters. The
+// vector based version returns offsets ordered by parameter. For example if
+// invoked with a and b offsets[0] gives the offset for a and offsets[1] the
+// offset of b regardless of where the parameters end up in the string.
+NSString* GetNSStringF(int message_id,
+                       const string16& a,
+                       const string16& b,
+                       std::vector<size_t>* offsets);
+
 // Same as GetNSString, but runs the result through FixUpWindowsStyleLabel
 // before returning it.
 NSString* GetNSStringWithFixup(int message_id);