Rename gpu_fuzzer backed by the NULL ANGLE backend.

Otherwise it will not be running on ClusterFuzz.

TBR=geofflang@chromium.org, inferno@chromium.org
BUG=
CQ_INCLUDE_TRYBOTS=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

Review-Url: https://codereview.chromium.org/2570493002
Cr-Commit-Position: refs/heads/master@{#437909}

gpu/BUILD.gn

@@ -402,7 +402,7 @@ fuzzer_test("gpu_fuzzer") {
   libfuzzer_options = [ "max_len=16384" ]
 }
 
-fuzzer_test("gpu_fuzzer_angle") {
+fuzzer_test("gpu_angle_fuzzer") {
   sources = [
     "command_buffer/tests/fuzzer_main.cc",
   ]