Add support for glMapBufferRange. Use glMapBufferRange and glMapBufferSubData.

src/gpu/gl/debug/GrBufferObj.h

Index: src/gpu/gl/debug/GrBufferObj.h
diff --git a/src/gpu/gl/debug/GrBufferObj.h b/src/gpu/gl/debug/GrBufferObj.h
index fecfeb5e3ceb75607e3baefb5c71127176e3accb..05d3cfddde04a33a91a59eb1f46bf740cfc49daa 100644
--- a/src/gpu/gl/debug/GrBufferObj.h
+++ b/src/gpu/gl/debug/GrBufferObj.h
@@ -34,9 +34,15 @@ public:
         GrAlwaysAssert(!fMapped);
     }
 
-    void setMapped()             { fMapped = true; }
+    void setMapped(GrGLintptr offset, GrGLsizeiptr length) {
+        fMapped = true;
+        fMappedOffset = offset;
+        fMappedLength = length;
+    }
     void resetMapped()           { fMapped = false; }
     bool getMapped() const       { return fMapped; }
+    GrGLsizei getMappedOffset() const { return fMappedOffset; }
+    GrGLsizei getMappedLength() const { return fMappedLength; }
 
     void setBound()              { fBound = true; }
     void resetBound()            { fBound = false; }
@@ -55,7 +61,9 @@ protected:
 private:
 
     GrGLchar*    fDataPtr;
-    bool         fMapped;       // is the buffer object mapped via "glMapBuffer"?
+    bool         fMapped;       // is the buffer object mapped via "glMapBuffer[Range]"?
+    GrGLintptr   fMappedOffset; // the offset of the buffer range that is mapped
+    GrGLsizeiptr fMappedLength; // the size of the buffer range that is mapped
     bool         fBound;        // is the buffer object bound via "glBindBuffer"?
     GrGLsizeiptr fSize;         // size in bytes
     GrGLint      fUsage;        // one of: GL_STREAM_DRAW,