Use GLSLCaps for creating processor keys and GLSL-specific programs

Effectively all this does is future-proof any GLSL-specific code, as
GLSLCaps is just a typedef of GLCaps.

BUG=skia:

Review URL: https://codereview.chromium.org/1109863004
diff --git a/src/gpu/GrPrimitiveProcessor.h b/src/gpu/GrPrimitiveProcessor.h
index 45668e9..ea1237b 100644
--- a/src/gpu/GrPrimitiveProcessor.h
+++ b/src/gpu/GrPrimitiveProcessor.h
@@ -68,6 +68,7 @@
 
 class GrIndexBufferAllocPool;
 class GrGLCaps;
+typedef GrGLCaps GrGLSLCaps;
 class GrGLPrimitiveProcessor;
 class GrVertexBufferAllocPool;
 
@@ -163,7 +164,7 @@
      * processor's GL backend implementation.
      */
     virtual void getGLProcessorKey(const GrBatchTracker& bt,
-                                   const GrGLCaps& caps,
+                                   const GrGLSLCaps& caps,
                                    GrProcessorKeyBuilder* b) const = 0;
 
 
@@ -171,7 +172,7 @@
         for the given GrProcessor; caller is responsible for deleting
         the object. */
     virtual GrGLPrimitiveProcessor* createGLInstance(const GrBatchTracker& bt,
-                                                     const GrGLCaps& caps) const = 0;
+                                                     const GrGLSLCaps& caps) const = 0;
 
     bool isPathRendering() const { return fIsPathRendering; }