Fix sanitizer in setViewportAndProjection.

On integer sanitized builds calculating b (and possibly t) throws a
runtime error due to an unsigned integer overflow occuring.

 runtime error: unsigned integer overflow: 1024 - 1920 cannot be
 represented in type 'unsigned long'

This changes the type of b (and others) to int32_t, which matches the
types in Rect and can store the negative results above without
overflowing.

Bug: 30969751
Test: Compiles, surfaceflinger tests pass.
Change-Id: Ifb45e3c7e14a2f782412e65d56e462e7df37faba
diff --git a/services/surfaceflinger/RenderEngine/GLES20RenderEngine.cpp b/services/surfaceflinger/RenderEngine/GLES20RenderEngine.cpp
index 3161888..d1ee6f8 100644
--- a/services/surfaceflinger/RenderEngine/GLES20RenderEngine.cpp
+++ b/services/surfaceflinger/RenderEngine/GLES20RenderEngine.cpp
@@ -154,12 +154,12 @@
 void GLES20RenderEngine::setViewportAndProjection(size_t vpw, size_t vph, Rect sourceCrop,
                                                   size_t hwh, bool yswap,
                                                   Transform::orientation_flags rotation) {
-    size_t l = sourceCrop.left;
-    size_t r = sourceCrop.right;
+    int32_t l = sourceCrop.left;
+    int32_t r = sourceCrop.right;
 
     // In GL, (0, 0) is the bottom-left corner, so flip y coordinates
-    size_t t = hwh - sourceCrop.top;
-    size_t b = hwh - sourceCrop.bottom;
+    int32_t t = hwh - sourceCrop.top;
+    int32_t b = hwh - sourceCrop.bottom;
 
     mat4 m;
     if (yswap) {