Enable init'ed but unused var warning on windows for closer parity with mac/linux warnings.

src/views/win/SkOSWindow_win.cpp

Index: src/views/win/SkOSWindow_win.cpp
===================================================================
--- src/views/win/SkOSWindow_win.cpp	(revision 8271)
+++ src/views/win/SkOSWindow_win.cpp	(working copy)
@@ -202,7 +202,7 @@
         //       buffer before passing to SetDIBitsToDevice().
         SkASSERT(bitmap.width() * bitmap.bytesPerPixel() == bitmap.rowBytes());
         bitmap.lockPixels();
-        int iRet = SetDIBitsToDevice(hdc,
+        int ret = SetDIBitsToDevice(hdc,
             0, 0,
             bitmap.width(), bitmap.height(),
             0, 0,
@@ -210,6 +210,7 @@
             bitmap.getPixels(),
             &bmi,
             DIB_RGB_COLORS);
+        (void)ret; // we're ignoring potential failures for now.
         bitmap.unlockPixels();
     }
 }