Fix and enable warning C4244 (Conversion from 'type1' to 'type2', possible loss of data)

Change-Id: Id0e06d7d6600344d858f00dabc219d79289bbc82
Reviewed-on: https://chromium-review.googlesource.com/265020
Tested-by: Minmin Gong <mgong@microsoft.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/tests/end2end_tests/BufferDataTest.cpp b/src/tests/end2end_tests/BufferDataTest.cpp
index 7f47935..5dcf29f 100644
--- a/src/tests/end2end_tests/BufferDataTest.cpp
+++ b/src/tests/end2end_tests/BufferDataTest.cpp
@@ -362,7 +362,7 @@
     uint8_t srcBytes[numBytes];
     for (size_t i = 0; i < numBytes; ++i)
     {
-        srcBytes[i] = i;
+        srcBytes[i] = static_cast<uint8_t>(i);
     }
 
     void *dest = glMapBufferRange(GL_ARRAY_BUFFER, 0, numBytes, GL_MAP_WRITE_BIT | GL_MAP_INVALIDATE_BUFFER_BIT);