Optimize posting of WTF::Closure and improve scheduler test mocks

third_party/WebKit/public/platform/WebTaskRunner.h

Index: third_party/WebKit/public/platform/WebTaskRunner.h
diff --git a/third_party/WebKit/public/platform/WebTaskRunner.h b/third_party/WebKit/public/platform/WebTaskRunner.h
index 6e2bbd8e1647d3efd65dbe8562dcb11905a83621..9c8092064b0c996bf0adc709da58b5fc906cb46d 100644
--- a/third_party/WebKit/public/platform/WebTaskRunner.h
+++ b/third_party/WebKit/public/platform/WebTaskRunner.h
@@ -7,6 +7,7 @@
 
 #include "WebCommon.h"
 #include "public/platform/WebTraceLocation.h"
+#include "public/platform/scheduler/base/task_queue.h"
 #include <memory>
 
 #ifdef INSIDE_BLINK
@@ -22,10 +23,14 @@ namespace blink {
 using SingleThreadTaskRunner = base::SingleThreadTaskRunner;
 
 // The blink representation of a chromium SingleThreadTaskRunner.
+// TODO(alexclarke): Rename to PlatformTaskRunner and move onto the oilpan heap.
+// TODO(alexclarke): Consider using base::TimeDelta for the delays. (crbug.com/402027)
 class BLINK_PLATFORM_EXPORT WebTaskRunner {
 public:
     virtual ~WebTaskRunner() {}
 
+    using TaskHandle = scheduler::TaskQueue::TaskHandle;
+
     class BLINK_PLATFORM_EXPORT Task {
     public:
         virtual ~Task() { }
@@ -40,6 +45,19 @@ public:
     // Takes ownership of |Task|. Can be called from any thread.
     virtual void postDelayedTask(const WebTraceLocation&, Task*, double delayMs) = 0;
 
+    // Posts the given task to be run after |delay| has passed. Returns a handle
+    // which can be passed to cancelTask to cancel the task before it has run.
+    // Note this must be called from the thread the tasks are run on (i.e the
+    // thread where runsTasksOnCurrentThread returns true).
+    virtual TaskHandle postCancellableDelayedTask(const tracked_objects::Location&, const base::Closure&, double delayMs) = 0;

[alex clarke (OOO till 29th), 2016/08/22 17:43:01]

Daniel on the other patch you expressed some API concerns. Are you OK with us
adding this? If further discussion is needed, I could split this off onto a
separate patch. 

+
+    // Attempts to cancel a task posted by PostCancellableDelayedTask. Returns
+    // true on success or false otherwise. Note this will fail unless called on
+    // the same WebTaskRunner that was used to post the task. Note this must be
+    // called from the thread the tasks are run on (i.e the thread where
+    // runsTasksOnCurrentThread returns true).
+    virtual bool cancelTask(const TaskHandle&) = 0;
+
     // Returns a clone of the WebTaskRunner.
     virtual std::unique_ptr<WebTaskRunner> clone() = 0;
 
@@ -66,7 +84,7 @@ public:
     virtual double monotonicallyIncreasingVirtualTimeSeconds() const = 0;
 
     // Returns the underlying task runner object.
-    virtual SingleThreadTaskRunner* taskRunner() = 0;
+    virtual SingleThreadTaskRunner* toSingleThreadTaskRunner() = 0;
 
 #ifdef INSIDE_BLINK
     // Helpers for posting bound functions as tasks.
@@ -78,6 +96,12 @@ public:
     // For same-thread posting. Must be called from the associated WebThread.
     void postTask(const WebTraceLocation&, std::unique_ptr<WTF::Closure>);
     void postDelayedTask(const WebTraceLocation&, std::unique_ptr<WTF::Closure>, long long delayMs);
+
+    // Posts the given same-thread closure to be run after |delay| has passed.
+    // Returns a handle which can be passed to cancelTask to cancel the task
+    // before it has run. Note this must be called from the thread the tasks are
+    // run on (i.e the thread where runsTasksOnCurrentThread returns true).
+    TaskHandle postCancellableDelayedTask(const WebTraceLocation&, std::unique_ptr<WTF::Closure>, double delayMs);
 #endif
 };