Minor IPC fuzzer fixes:

1) Favor --renderer-cmd-prefix more heavil when generating flags files
for ClusterFuzz.
2) Remove the --gpu-launcher option as it no longer works. Looking at
existing issues I'm not sure that this is too important for our
coverage, so it seems easier to remove it than to try to continue
maintaining it.

R=inferno@chromium.org

Bug: 904773
Change-Id: I3f0f468337540dfc5af73289ad0a46e41dcdb5ae
Reviewed-on: https://chromium-review.googlesource.com/c/1340978Reviewed-by: Abhishek Arya <inferno@chromium.org>
Commit-Queue: Abhishek Arya <inferno@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609703}

tools/ipc_fuzzer/scripts/play_testcase.py

@@ -87,7 +87,6 @@ def main():
 
   prefixes = {
       '--renderer-cmd-prefix',
-      '--gpu-launcher',
       '--plugin-launcher',
       '--ppapi-plugin-launcher',
       '--utility-cmd-prefix',

tools/ipc_fuzzer/scripts/utils.py

@@ -17,11 +17,13 @@ FUZZ_PREFIX = 'fuzz-'
 IPC_FUZZER_APPLICATION = 'ipc_fuzzer'
 IPC_REPLAY_APPLICATION = 'ipc_fuzzer_replay'
 IPCDUMP_EXTENSION = '.ipcdump'
-LAUNCH_PREFIXES = [
-    '--gpu-launcher',
+UNCOMMON_PREFIX_CHANCE = 10  # 1 in 10
+COMMON_LAUNCH_PREFIXES = [
+    '--renderer-cmd-prefix',
+]
+UNCOMMON_LAUNCH_PEFIXES = [
     '--plugin-launcher',
     '--ppapi-plugin-launcher',
-    '--renderer-cmd-prefix',
     '--utility-cmd-prefix',
 ]
 
@@ -35,7 +37,10 @@ def application_name_for_platform(application_name):
 
 def create_flags_file(ipcdump_testcase_path):
   """Create a flags file to add launch prefix to application command line."""
-  random_launch_prefix = random.choice(LAUNCH_PREFIXES)
+  prefixes = (UNCOMMON_LAUNCH_PREFIXES if
+              random.randint(1, UNCOMMON_PREFIX_CHANCE) == 1 else
+              COMMON_LAUNCH_PREFIXES)
+  random_launch_prefix = random.choice(prefixes)
   application_name = application_name_for_platform(IPC_REPLAY_APPLICATION)
   file_content = '%s=%%APP_DIR%%%s%s' % (random_launch_prefix, os.path.sep,
                                          application_name)