cc: Simplify task and its derived classes.

cc/tiles/tile_manager_unittest.cc

Index: cc/tiles/tile_manager_unittest.cc
diff --git a/cc/tiles/tile_manager_unittest.cc b/cc/tiles/tile_manager_unittest.cc
index 531708102abe2bd66617015fd8fb4a1daddef95a..5383ca3f787a10dc7d91c9669de7aa7aa2b7ab17 100644
--- a/cc/tiles/tile_manager_unittest.cc
+++ b/cc/tiles/tile_manager_unittest.cc
@@ -1822,7 +1822,7 @@ TEST_F(TileManagerTest, LowResHasNoImage) {
 }
 
 // Fake TileTaskRunner that just no-ops all calls.
-class FakeTileTaskRunner : public TileTaskRunner, public TileTaskClient {
+class FakeTileTaskRunner : public TileTaskRunner, public DependencyTaskClient {
  public:
   FakeTileTaskRunner() {}
   ~FakeTileTaskRunner() override {}
@@ -1839,7 +1839,7 @@ class FakeTileTaskRunner : public TileTaskRunner, public TileTaskClient {
 
   void ScheduleTasks(TaskGraph* graph) override {}
 
-  // TileTaskClient methods.
+  // DependencyTaskClient methods.
   scoped_ptr<RasterBuffer> AcquireBufferForRaster(
       const Resource* resource,
       uint64_t resource_content_id,
@@ -1860,7 +1860,7 @@ class CancellingTileTaskRunner : public FakeTileTaskRunner {
     // Just call CompleteOnOriginThread on each item in the queue. As none of
     // these items have run yet, they will be treated as cancelled tasks.
     for (const auto& node : graph->nodes) {
-      static_cast<TileTask*>(node.task)->CompleteOnOriginThread(this);
+      node.task->CompleteOnOriginThread(this);
     }
   }
 };
@@ -1935,7 +1935,7 @@ class VerifyResourceContentIdTileTaskRunner : public FakeTileTaskRunner {
 
   void ScheduleTasks(TaskGraph* graph) override {
     for (const auto& node : graph->nodes) {
-      TileTask* task = static_cast<TileTask*>(node.task);
+      DependencyTask* task = node.task;
       // Triggers a call to AcquireBufferForRaster.
       task->ScheduleOnOriginThread(this);
       // Calls TileManager as though task was cancelled.
@@ -1943,7 +1943,7 @@ class VerifyResourceContentIdTileTaskRunner : public FakeTileTaskRunner {
     }
   }
 
-  // TileTaskClient methods.
+  // DependencyTaskClient methods.
   scoped_ptr<RasterBuffer> AcquireBufferForRaster(
       const Resource* resource,
       uint64_t resource_content_id,