Fix signed/unsigned missmatch on 32-bit builds.

BUG=angle:681

Change-Id: I6144359acd1611a13b0a582d3a31019138bb941c
Reviewed-on: https://chromium-review.googlesource.com/239844
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/renderer/d3d/TextureD3D.cpp b/src/libANGLE/renderer/d3d/TextureD3D.cpp
index d0c27c1..b53ef6c 100644
--- a/src/libANGLE/renderer/d3d/TextureD3D.cpp
+++ b/src/libANGLE/renderer/d3d/TextureD3D.cpp
@@ -800,7 +800,7 @@
 {
     ASSERT(GL_TEXTURE_2D && size.depth == 1);
 
-    for (int level = 0; level < levels; level++)
+    for (size_t level = 0; level < levels; level++)
     {
         gl::Extents levelSize(std::max(1, size.width >> level),
                               std::max(1, size.height >> level),
@@ -1334,7 +1334,7 @@
     ASSERT(size.width == size.height);
     ASSERT(size.depth == 1);
 
-    for (int level = 0; level < levels; level++)
+    for (size_t level = 0; level < levels; level++)
     {
         GLsizei mipSize = std::max(1, size.width >> level);
         for (int faceIndex = 0; faceIndex < 6; faceIndex++)
@@ -1920,7 +1920,7 @@
 {
     ASSERT(target == GL_TEXTURE_3D);
 
-    for (int level = 0; level < levels; level++)
+    for (size_t level = 0; level < levels; level++)
     {
         gl::Extents levelSize(std::max(1, size.width >> level),
                               std::max(1, size.height >> level),
@@ -2454,7 +2454,7 @@
 
     deleteImages();
 
-    for (int level = 0; level < gl::IMPLEMENTATION_MAX_TEXTURE_LEVELS; level++)
+    for (size_t level = 0; level < gl::IMPLEMENTATION_MAX_TEXTURE_LEVELS; level++)
     {
         gl::Extents levelLayerSize(std::max(1, size.width >> level),
                                    std::max(1, size.height >> level),