[Benchmark] Crash happened when running WebDNN with VGG16 model on Android

[Christywl]

Test benchmark with 7befcda, crash happened when running WebDNN with VGG16 model with Google Chrome Stable 69.0.3497.91 on Android:

• WebDNN(WebGL backend) + VGG16
• WebDNN(WebGL backend + Optimize) + VGG16
• WebDNN(WASM backend) + VGG16
• WebDNN(WASM backend + Optimize) + VGG16

Crash log:
webdnn_crash.log