Batch consecutive draw rects.

Review URL: http://codereview.appspot.com/4178057/

git-svn-id: http://skia.googlecode.com/svn/trunk@800 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gpu/include/GrIndexBuffer.h b/gpu/include/GrIndexBuffer.h
index 85ff749..09d1977 100644
--- a/gpu/include/GrIndexBuffer.h
+++ b/gpu/include/GrIndexBuffer.h
@@ -21,6 +21,13 @@
 #include "GrGeometryBuffer.h"
 
 class GrIndexBuffer : public GrGeometryBuffer {
+public:
+        /**
+         * Retrieves the maximum number of quads that could be rendered
+         * from the index buffer (using kTriangles_PrimitiveType).
+         * @return the maximum number of quads using full size of index buffer.
+         */
+        int maxQuads() const { return size() / (sizeof(uint16_t) * 6); }
 protected:
     GrIndexBuffer(size_t sizeInBytes, bool dynamic) :
         INHERITED(sizeInBytes, dynamic) {}