Fix debug standalone build warning on MSVS 2015

Fixes signed/unsigned mismatch due to missing type cast inside an
assert.

BUG=angleproject:1382
TEST=standalone MSVS 2015 debug build

Change-Id: I1508b54a2608e9204ad582bde4bd62af6926c36e
Reviewed-on: https://chromium-review.googlesource.com/360921
Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>

src/libANGLE/renderer/gl/ProgramGL.cpp

@@ -542,7 +542,7 @@ void ProgramGL::postLink()
             kQueryProperties, static_cast<GLsizei>(ArraySize(queryResults)), &queryLength,
             queryResults);
 
-        ASSERT(queryLength == ArraySize(kQueryProperties));
+        ASSERT(queryLength == static_cast<GLsizei>(ArraySize(kQueryProperties)));
 
         PathRenderingFragmentInput baseElementInput;
         baseElementInput.name     = name;