Add an on-screen overdraw counter

The counter can be enabled by setting the system property called
debug.hwui.overdraw to the string "count". If the string is set
to "show", overdraw will be highlighted on screen instead of
printing out a simple counter.

Change-Id: I9a9c970d54bffab43138bbb7682f6c04bc2c40bd
diff --git a/libs/hwui/Program.h b/libs/hwui/Program.h
index a252209..dd1aaa2 100644
--- a/libs/hwui/Program.h
+++ b/libs/hwui/Program.h
@@ -85,6 +85,7 @@
 #define PROGRAM_HAS_COLORS 42
 
 #define PROGRAM_HAS_DEBUG_HIGHLIGHT 43
+#define PROGRAM_EMULATE_STENCIL 44
 
 ///////////////////////////////////////////////////////////////////////////////
 // Types
@@ -163,6 +164,7 @@
     float gamma;
 
     bool hasDebugHighlight;
+    bool emulateStencil;
 
     /**
      * Resets this description. All fields are reset back to the default
@@ -275,6 +277,7 @@
         if (isSimpleGradient) key |= programid(0x1) << PROGRAM_IS_SIMPLE_GRADIENT;
         if (hasColors) key |= programid(0x1) << PROGRAM_HAS_COLORS;
         if (hasDebugHighlight) key |= programid(0x1) << PROGRAM_HAS_DEBUG_HIGHLIGHT;
+        if (emulateStencil) key |= programid(0x1) << PROGRAM_EMULATE_STENCIL;
         return key;
     }