[api][cleanup] Mark Call*OnForegroundThread as V8_DEPRECATE_SOON

These functions got replaced the the taskrunner API. The new way to
post tasks is as follows:

v8::Platform* platform = ...; // e.g. V8::GetCurrentPlatform();
v8::Isolate* = ...;

std::shared_ptr<v8::TaskRunner> taskrunner = platform->GetForegroundTaskRunner(isolate);
std::unique_ptr<v8::Task> task = ...;

taskrunner->PostTask(std::move(task));

R=ulan@chromium.org

Bug: v8:8238
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I44a70fc530daae581ee31e54fd09e776ba648406
Reviewed-on: https://chromium-review.googlesource.com/c/1261936Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56400}

include/v8-platform.h

@@ -322,7 +322,9 @@ class Platform {
    * |isolate|. Tasks posted for the same isolate should be execute in order of
    * scheduling. The definition of "foreground" is opaque to V8.
    */
-  virtual void CallOnForegroundThread(Isolate* isolate, Task* task) = 0;
+  V8_DEPRECATE_SOON(
+      "Use a taskrunner acquired by GetForegroundTaskRunner instead.",
+      virtual void CallOnForegroundThread(Isolate* isolate, Task* task)) = 0;
 
   /**
    * Schedules a task to be invoked on a foreground thread wrt a specific
@@ -330,8 +332,10 @@ class Platform {
    * Tasks posted for the same isolate should be execute in order of
    * scheduling. The definition of "foreground" is opaque to V8.
    */
-  virtual void CallDelayedOnForegroundThread(Isolate* isolate, Task* task,
-                                             double delay_in_seconds) = 0;
+  V8_DEPRECATE_SOON(
+      "Use a taskrunner acquired by GetForegroundTaskRunner instead.",
+      virtual void CallDelayedOnForegroundThread(Isolate* isolate, Task* task,
+                                                 double delay_in_seconds)) = 0;
 
   /**
    * Schedules a task to be invoked on a foreground thread wrt a specific
@@ -341,7 +345,10 @@ class Platform {
    * starved for an arbitrarily long time if no idle time is available.
    * The definition of "foreground" is opaque to V8.
    */
-  virtual void CallIdleOnForegroundThread(Isolate* isolate, IdleTask* task) {
+  V8_DEPRECATE_SOON(
+      "Use a taskrunner acquired by GetForegroundTaskRunner instead.",
+      virtual void CallIdleOnForegroundThread(Isolate* isolate,
+                                              IdleTask* task)) {
     // This must be overriden if |IdleTasksEnabled()|.
     abort();
   }

src/d8.cc

@@ -231,12 +231,14 @@ class PredictablePlatform : public Platform {
   }
 
   void CallOnForegroundThread(v8::Isolate* isolate, Task* task) override {
-    platform_->CallOnForegroundThread(isolate, task);
+    // This is a deprecated function and should not be called anymore.
+    UNREACHABLE();
   }
 
   void CallDelayedOnForegroundThread(v8::Isolate* isolate, Task* task,
                                      double delay_in_seconds) override {
-    platform_->CallDelayedOnForegroundThread(isolate, task, delay_in_seconds);
+    // This is a deprecated function and should not be called anymore.
+    UNREACHABLE();
   }
 
   void CallIdleOnForegroundThread(Isolate* isolate, IdleTask* task) override {

test/cctest/cctest.h

@@ -684,13 +684,14 @@ class TestPlatform : public v8::Platform {
   }
 
   void CallOnForegroundThread(v8::Isolate* isolate, v8::Task* task) override {
-    old_platform_->CallOnForegroundThread(isolate, task);
+    // This is a deprecated function and should not be called anymore.
+    UNREACHABLE();
   }
 
   void CallDelayedOnForegroundThread(v8::Isolate* isolate, v8::Task* task,
                                      double delay_in_seconds) override {
-    old_platform_->CallDelayedOnForegroundThread(isolate, task,
-                                                 delay_in_seconds);
+    // This is a deprecated function and should not be called anymore.
+    UNREACHABLE();
   }
 
   double MonotonicallyIncreasingTime() override {
@@ -703,7 +704,8 @@ class TestPlatform : public v8::Platform {
 
   void CallIdleOnForegroundThread(v8::Isolate* isolate,
                                   v8::IdleTask* task) override {
-    old_platform_->CallIdleOnForegroundThread(isolate, task);
+    // This is a deprecated function and should not be called anymore.
+    UNREACHABLE();
   }
 
   bool IdleTasksEnabled(v8::Isolate* isolate) override {