Remove default NOP implementation of MonotonicallyIncreasingTime.

include/v8-platform.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_V8_PLATFORM_H_
 #define V8_V8_PLATFORM_H_
 
 namespace v8 {
 
 class Isolate;
@@ skipping 38 matching lines @@
   virtual void CallOnBackgroundThread(Task* task,
                                       ExpectedRuntime expected_runtime) = 0;
 
   /**
    * Schedules a task to be invoked on a foreground thread wrt a specific
    * |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;
 
-
   /**
    * Monotonically increasing time in seconds from an arbitrary fixed point in
    * the past. This function is expected to return at least
    * millisecond-precision values. For this reason,
    * it is recommended that the fixed point be no further in the past than
    * the epoch.
    **/
-  virtual double MonotonicallyIncreasingTime() {
-    // TODO(rmcilroy): Remove this default implementation when Chromium
-    // change has landed.
-    return 0;
-  }
+  virtual double MonotonicallyIncreasingTime() = 0;
 };
 
 }  // namespace v8
 
 #endif  // V8_V8_PLATFORM_H_