Re-land: gpu: Add CHROMIUM_sync_query extension.

gpu/GLES2/extensions/CHROMIUM/CHROMIUM_sync_query.txt

+Name
+
+    CHROMIUM_sync_query
+
+Name Strings
+
+    GL_CHROMIUM_sync_query
+
+Version
+
+    Last Modifed Date: April 15, 2014
+
+Dependencies
+
+    OpenGL ES 2.0 is required.
+
+    EXT_occlusion_query_boolean is required.
+
+Overview
+
+    This extension provides a query mechanism that allow for synchronization
+    between the host CPU and the GPU, which may be accessing the same
+    resources (typically memory).
+
+    This extension is useful in conjunction with CHROMIUM_map_image to
+    determine when it is safe to access a mapped image. Once the result of
+    a COMMANDS_COMPLETED_CHROMIUM query is available, all drawing commands
+    issued before the query must have finished. This ensures that the memory
+    corresponding to the issued commands can be safely modified (assuming no
+    other outstanding drawing commands are issued subsequent to the query).
+
+New Procedures and Functions
+
+    None.
+
+Errors
+
+    None.
+
+New Tokens
+
+    Accepted by the <target> parameter of BeginQueryEXT, EndQueryEXT,
+    and GetQueryivEXT:
+
+        COMMANDS_COMPLETED_CHROMIUM                     0x84F7
+
+New State
+
+    None.
+
+Revision History
+
+    4/15/2014   Documented the extension