Suppress cast warnings for active textures mask

Bug: angleproject:2747
Bug: angleproject:2763

Change-Id: I19f9e5ba760d3b5baf3997284523ee1db6bb8166
Reviewed-on: https://chromium-review.googlesource.com/1172206
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jie A Chen <jie.a.chen@intel.com>
diff --git a/src/libANGLE/State.cpp b/src/libANGLE/State.cpp
index 27d7e93..2124ce5 100644
--- a/src/libANGLE/State.cpp
+++ b/src/libANGLE/State.cpp
@@ -2656,8 +2656,9 @@
     {
         TextureType textureType = textureTypes[textureUnitIndex];
 
-        Texture *texture = getSamplerTexture(textureUnitIndex, textureType);
-        Sampler *sampler = getSampler(textureUnitIndex);
+        Texture *texture =
+            getSamplerTexture(static_cast<unsigned int>(textureUnitIndex), textureType);
+        Sampler *sampler = getSampler(static_cast<GLuint>(textureUnitIndex));
         ASSERT(static_cast<size_t>(textureUnitIndex) < mActiveTexturesCache.size());
         ASSERT(static_cast<size_t>(textureUnitIndex) < newActiveTextures.size());