Add glClientWaitSync to GPU command buffer.

gpu/command_buffer/common/gles2_cmd_format.h

Index: gpu/command_buffer/common/gles2_cmd_format.h
diff --git a/gpu/command_buffer/common/gles2_cmd_format.h b/gpu/command_buffer/common/gles2_cmd_format.h
index 944edfd5d0c639a497b95107e9a8ff4f197da49a..7ddff933e45ce4c6079e0a58d40c7e0b2c299704 100644
--- a/gpu/command_buffer/common/gles2_cmd_format.h
+++ b/gpu/command_buffer/common/gles2_cmd_format.h
@@ -43,6 +43,7 @@ typedef void GLvoid;
 typedef khronos_intptr_t GLintptr;
 typedef khronos_ssize_t  GLsizeiptr;
 typedef struct __GLsync *GLsync;
+typedef uint64_t GLuint64;
 
 namespace gpu {
 namespace gles2 {
@@ -77,6 +78,31 @@ static_assert(kTextures == 4, "kTextures should equal 4");
 
 }  // namespace id_namespaces
 
+union GLuint64Union {

[piman, 2015/02/18 18:38:00]

Oh, actually, I missed the fact that this was a union.
Writing a member of the union and reading another one is undefined behavior in
C++.

Why does this need to be a union at all exactly? We can extract higher and lower
uints using shifts and masks, and reconstruct similarly (you can make helper
functions).

[Zhenyao Mo, 2015/02/18 19:10:37]

Thanks for catching this.  My understanding of union was apparently incorrect.

+  GLuint64Union(GLuint64 v64)
+      : param64(v64) {
+  }
+
+  GLuint64Union(uint32_t v32_0, uint32_t v32_1) {
+    param32.v0 = v32_0;
+    param32.v1 = v32_1;
+  }
+
+  GLuint64 param64;
+  struct {
+    uint32_t v0;
+    uint32_t v1;
+  } param32;
+};
+
+static_assert(sizeof(GLuint64Union) == 8, "size of GLuint64Union should be 8");
+static_assert(offsetof(GLuint64Union, param64) == 0,
+              "offset of GLuint64Union.param64 should be 0");
+static_assert(offsetof(GLuint64Union, param32.v0) == 0,
+              "offset of GLuint64Union.param32.v0 should be 0");
+static_assert(offsetof(GLuint64Union, param32.v1) == 4,
+              "offset of GLuint64Union.param32.v1 should be 4");
+
 // Used for some glGetXXX commands that return a result through a pointer. We
 // need to know if the command succeeded or not and the size of the result. If
 // the command failed its result size will 0.