Use https when downloading linux sysroot images,

BUG=592204

Review URL: https://codereview.chromium.org/1766923002

Cr-Original-Commit-Position: refs/heads/master@{#379481}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: f9b847f035e9a55887867e8b0b3c0bde7fe0fc0d

linux/sysroot_scripts/install-sysroot.py

@@ -32,7 +32,7 @@ import gyp_chromium
 import gyp_environment
 
 
-URL_PREFIX = 'http://commondatastorage.googleapis.com'
+URL_PREFIX = 'https://commondatastorage.googleapis.com'
 URL_PATH = 'chrome-linux-sysroot/toolchain'
 REVISION_AMD64 = 'c52471d9dec240c8d0a88fa98aa1eefeee32e22f'
 REVISION_ARM = 'c52471d9dec240c8d0a88fa98aa1eefeee32e22f'