Add future sync point methods to ContextSupport.

gpu/GLES2/extensions/CHROMIUM/CHROMIUM_future_sync_point.txt

+Name
+
+    CHROMIUM_future_sync_point
+
+Name Strings
+
+    GL_CHROMIUM_future_sync_point
+
+Version
+
+    Last Modifed Date: July 14, 2014
+
+Dependencies
+
+    OpenGL ES 2.0 is required.
+    This extension depends on CHROMIUM_sync_point
+
+Overview
+
+    This extension allows sync points to be created that won't be retired
+    immediately.
+
+Issues
+
+    None
+
+New Tokens
+
+    None
+
+New Procedures and Functions
+
+    The command
+
+        uint InsertFutureSyncPointCHROMIUM()
+
+    creates a sync point, but does not insert it into the stream of commands.
+    The returned sync point name can be waited on immediately, but will not be
+    signalled until a retire command is sent, or until the context is
+    destroyed, whichever happens first.
+
+    The command
+
+        void RetireSyncPointCHROMIUM(uint sync_point)
+
+    causes a sync point to be signaled as soon as the previous commands have
+    been submitted to the server. The sync point named <sync_point> must have
+    been returned by InsertFutureSyncPointCHROMIUM. The sync point name will
+    be implicitly deleted when it becomes signaled.
+
+Errors
+
+    None.
+
+New State
+
+    None.
+
+Revision History
+
+    7/14/2014     Initial documentation.