initClassID no longer auto-allocates ids

Auto-allocated IDs mean that the IDs depend upon the order in which
classes happen to get initialized and are therefore not consistent
from run to run. This change paves the way for a persistent shader
cache by fixing the IDs in an enum.

Bug: skia:
Change-Id: I3e923c6c54f41b3b3eb616458abee83e0909c09f
Reviewed-on: https://skia-review.googlesource.com/56401
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/src/gpu/GrPrimitiveProcessor.h b/src/gpu/GrPrimitiveProcessor.h
index eb59d98..375b512 100644
--- a/src/gpu/GrPrimitiveProcessor.h
+++ b/src/gpu/GrPrimitiveProcessor.h
@@ -52,6 +52,9 @@
         InputRate            fInputRate;
     };
 
+    GrPrimitiveProcessor(ClassID classID)
+    : GrResourceIOProcessor(classID) {}
+
     int numAttribs() const { return fAttribs.count(); }
     const Attribute& getAttrib(int index) const { return fAttribs[index]; }