[inspector] Fix js_protocol.pdl build dependency

The master protocol description file is js_protocol.pdl, not .json

TBR=yangguo@chromium.org

Change-Id: Ibaef314a63c3e1665ed56bc8c66ca18a00c7fd4f
Reviewed-on: https://chromium-review.googlesource.com/c/1489976Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59882}

gni/v8.gni

@@ -81,7 +81,7 @@ if (v8_enable_backtrace == "") {
 # subdirectories.
 v8_path_prefix = get_path_info("../", "abspath")
 
-v8_inspector_js_protocol = v8_path_prefix + "/src/inspector/js_protocol.json"
+v8_inspector_js_protocol = v8_path_prefix + "/src/inspector/js_protocol.pdl"
 
 ###############################################################################
 # Templates

src/inspector/inspector_protocol_config.json

 {
     "protocol": {
-        "path": "js_protocol.json",
+        "path": "js_protocol.pdl",
         "package": "src/inspector/protocol",
         "output": "protocol",
         "namespace": ["v8_inspector", "protocol"],