Work on getting things built with -Wimplicit-fallthrough. This CL was uploaded by git cl split.

Bug: 177475
R=reveman@chromium.org

Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I5466428563e9e1f785a0c977368a6861432e734f
Reviewed-on: https://chromium-review.googlesource.com/889723Reviewed-by: David Reveman <reveman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532877}

gpu/perftests/texture_upload_perftest.cc

@@ -149,6 +149,7 @@ bool CompareBufferToRGBABuffer(GLenum format,
         case GL_LUMINANCE:  // (L_t, L_t, L_t, 1)
           expected[1] = pixels[pixels_index];
           expected[2] = pixels[pixels_index];
+          FALLTHROUGH;
         case GL_RED:  // (R_t, 0, 0, 1)
           expected[0] = pixels[pixels_index];
           expected[3] = 255;