ppapi: Always specify thread affinity when posting tasks

*** Note: There is no behavior change from this patch. ***

The PostTask APIs will shortly be changed to require all tasks to explicitly
specify their thread affinity, i.e., whether the task should run on the thread
pool or a specific named thread such as a BrowserThread. This patch updates all
call sites with thread affinity annotation. We also remove the "WithTraits"
suffix to make the call sites more readable.

Before:

    // Thread pool task.
    base::PostTaskWithTraits(FROM_HERE, {...}, ...);

    // UI thread task.
    base::PostTaskWithTraits(FROM_HERE, {BrowserThread::UI, ...}, ...);

After:

    // Thread pool task.
    base::PostTask(FROM_HERE, {base::ThreadPool(), ...}, ...);

    // UI thread task.
    base::PostTask(FROM_HERE, {BrowserThread::UI, ...}, ...);

This patch was semi-automatically prepared with these steps:

    1. Patch in https://chromium-review.googlesource.com/c/chromium/src/+/1635827
       to make thread affinity a build-time requirement.
    2. Run an initial pass with a clang rewriter:
       https://chromium-review.googlesource.com/c/chromium/src/+/1635623
    3. ninja -C out/Debug | grep 'requested here' | cut -d: -f1-3 | sort | \
           uniq > errors.txt
    4. while read line; do
         f=$(echo $line | cut -d: -f 1)
         r=$(echo $line | cut -d: -f 2)
         c=$(echo $line | cut -d: -f 3)
         sed -i "${r}s/./&base::ThreadPool(),/$c" $f
       done < errors.txt
    5. GOTO 3 until build succeeds.
    6. Remove the "WithTraits" suffix from task API call sites:

       $ tools/git/mffr.py -i <(cat <<EOF
       [
         ["PostTaskWithTraits",                            "PostTask"],
         ["PostDelayedTaskWithTraits",                     "PostDelayedTask"],
         ["PostTaskWithTraitsAndReply",                    "PostTaskAndReply"],
         ["CreateTaskRunnerWithTraits",                    "CreateTaskRunner"],
         ["CreateSequencedTaskRunnerWithTraits",           "CreateSequencedTaskRunner"],
         ["CreateUpdateableSequencedTaskRunnerWithTraits", "CreateUpdateableSequencedTaskRunner"],
         ["CreateSingleThreadTaskRunnerWithTraits",        "CreateSingleThreadTaskRunner"],
         ["CreateCOMSTATaskRunnerWithTraits",              "CreateCOMSTATaskRunner"]
       ]
       EOF
       )

This CL was uploaded by git cl split.

R=bbudge@chromium.org

Bug: 968047
Change-Id: Ifb12f9278a02a0a821a6b92cb6625cf6e57d8b31
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1728885
Auto-Submit: Sami Kyöstilä <skyostil@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683273}

ppapi/host/resource_message_filter.h

@@ -52,7 +52,7 @@ struct PPAPI_HOST_EXPORT ResourceMessageFilterDeleteTraits {
 //   scoped_refptr<base::TaskRunner> OverrideTaskRunnerForMessage(
 //       const IPC::Message& message) override {
 //     if (message.type() == MyMessage::ID) {
-//       return base::CreateSingleThreadTaskRunnerWithTraits(
+//       return base::CreateSingleThreadTaskRunner(
 //           {BrowserThread::UI});
 //     }
 //     return NULL;