Move implementation from header to source.

base/task.h

Index: base/task.h
diff --git a/base/task.h b/base/task.h
index 142554601365c4509021b1129f268c981ae86a8e..660b4a44efb2a511236273f84a1d1a6fb1ecc7af 100644
--- a/base/task.h
+++ b/base/task.h
@@ -18,8 +18,8 @@
 
 class Task : public tracked_objects::Tracked {
  public:
-  Task() {}
-  virtual ~Task() {}
+  Task();
+  virtual ~Task();
 
   // Tasks are automatically deleted after Run is called.
   virtual void Run() = 0;
@@ -27,6 +27,9 @@ class Task : public tracked_objects::Tracked {
 
 class CancelableTask : public Task {
  public:
+  CancelableTask();
+  ~CancelableTask();

[Evan Martin, 2010/07/15 17:37:33]

Why are these needed?
Should this be virtual?

[Elliot Glaysher, 2010/07/15 18:08:10]

Because a copy of the synthesized constructor/destructor is still emitted in the
resulting object files. Task()/~Task()/CancelableTask()/~CancelableTask() were
some of the hotspots that showed up when I did my big script to find the most
commonly included weak symbols.
Done.

+
   // Not all tasks support cancellation.
   virtual void Cancel() = 0;
 };