Add implementation of MonotonicallyIncreasingTime to Gin's V8 platform implementation.

gin/v8_platform.cc

Index: gin/v8_platform.cc
diff --git a/gin/v8_platform.cc b/gin/v8_platform.cc
index d50ff24f8bf49d7aa2c947e6f4bb20a1cbaee6ab..ec163ded8d1444a06f18aa0164df754186633f3f 100644
--- a/gin/v8_platform.cc
+++ b/gin/v8_platform.cc
@@ -39,4 +39,9 @@ void V8Platform::CallOnForegroundThread(v8::Isolate* isolate, v8::Task* task) {
       FROM_HERE, base::Bind(&v8::Task::Run, base::Owned(task)));
 }
 
+double V8Platform::MonotonicallyIncreasingTime() {
+  return base::TimeTicks::Now().ToInternalValue() /
+      static_cast<double>(base::Time::kMicrosecondsPerSecond);
+}
+
 }  // namespace gin