Move flush id from WebGraphicsContext3DImpl to GLES2Implementation.

gpu/command_buffer/cmd_buffer_functions.txt

Index: gpu/command_buffer/cmd_buffer_functions.txt
diff --git a/gpu/command_buffer/cmd_buffer_functions.txt b/gpu/command_buffer/cmd_buffer_functions.txt
index 119f3f269498f41e9b6ccf29c0f5d24f8ca988cc..3f036613622ac75ade47ea67c6956bc57cefc705 100644
--- a/gpu/command_buffer/cmd_buffer_functions.txt
+++ b/gpu/command_buffer/cmd_buffer_functions.txt
@@ -316,6 +316,7 @@ GL_APICALL void         GL_APIENTRY glScheduleCALayerCHROMIUM (GLuint contents_t
 GL_APICALL void         GL_APIENTRY glCommitOverlayPlanesCHROMIUM (void);
 GL_APICALL void         GL_APIENTRY glSwapInterval (GLint interval);
 GL_APICALL void         GL_APIENTRY glFlushDriverCachesCHROMIUM (void);
+GL_APICALL GLuint       GL_APIENTRY glGetLastFlushIdCHROMIUM (void);
 
 // Extension CHROMIUM_path_rendering.
 GL_APICALL void         GL_APIENTRY glMatrixLoadfCHROMIUM (GLenumMatrixMode matrixMode, const GLfloat* m);