Issue 351: Reimplement OAuth2 (Step 3 - Tests, Flows and Credential)

Src/GoogleApis/Apis/Util/IClock.cs

Index: Src/GoogleApis/Apis/Util/IClock.cs
===================================================================
--- a/Src/GoogleApis/Apis/Util/IClock.cs
 b/Src/GoogleApis/Apis/Util/IClock.cs
@@ -26,6 26,12 @@
 /// expressed as the local time.
 /// </summary>
 DateTime Now { get; }
 /// <summary>
 /// Gets a <seealso cref="DateTime"/> object that is set to the current date and time on this computer,
 /// expressed as UTC time.
 /// </summary>
 DateTime UtcNow { get; }
 }
 /// <summary>A default clock implementation that wraps the <seealso cref="DateTime.Now"/> property.</summary>
@@ -41,5 47,10 @@
 {
 get { return DateTime.Now; }
 }
 public DateTime UtcNow
 {
 get { return DateTime.UtcNow; }
 }
 }
 }