Use a const_iterator in structsHeader().

This was breaking the build for some compilers (GCC on android).

Change-Id: Ibfe5603710961497b6c15aa2d9cb568096ca1dd4
Reviewed-on: https://chromium-review.googlesource.com/204897
Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
diff --git a/src/compiler/translator/StructureHLSL.cpp b/src/compiler/translator/StructureHLSL.cpp
index 1221f1e..caca224 100644
--- a/src/compiler/translator/StructureHLSL.cpp
+++ b/src/compiler/translator/StructureHLSL.cpp
@@ -449,7 +449,9 @@
         out << mStructDeclarations[structIndex];
     }
 
-    for (Constructors::iterator constructor = mConstructors.begin(); constructor != mConstructors.end(); constructor++)
+    for (Constructors::const_iterator constructor = mConstructors.begin();
+         constructor != mConstructors.end();
+         constructor++)
     {
         out << *constructor;
     }