Remove stale gn arg to avoid undeclared argument warning.

v8_enable_inspector was removed recently. Clean up remnants.

Also fixes a dependent gn check issue which blocked submission,
http://crrev.com/462467 did not update GN deps for new header.

BUG=645890,708965
TEST=none

Review-Url: https://codereview.chromium.org/2801123002
Cr-Commit-Position: refs/heads/master@{#462652}

.gn

@@ -41,7 +41,6 @@ default_args = {
     "//third_party/WebKit/Source/core/streams/WritableStream.js",
   ]
   v8_experimental_extra_library_files = []
-  v8_enable_inspector = true
   v8_enable_gdbjit = false
   v8_imminent_deprecation_warnings = false
 }

content/test/BUILD.gn

@@ -1651,6 +1651,7 @@ test("content_unittests") {
       "//third_party/opus",
       "//third_party/webrtc/api:libjingle_peerconnection",
       "//third_party/webrtc/api:rtc_stats_api",
+      "//third_party/webrtc/api/video_codecs:video_codecs_api",
       "//third_party/webrtc/base:rtc_base",
       "//third_party/webrtc/media:rtc_media",
       "//third_party/webrtc/modules/desktop_capture:primitives",

ios/BUILD.gn

@@ -13,7 +13,6 @@ declare_args() {
   # the overrides are never used.
   v8_extra_library_files = []
   v8_experimental_extra_library_files = []
-  v8_enable_inspector = true
   v8_enable_gdbjit = false
   v8_imminent_deprecation_warnings = false
 }
@@ -21,7 +20,6 @@ declare_args() {
 # Prevent warnings for unused build args above.
 assert(v8_extra_library_files != 0)
 assert(v8_experimental_extra_library_files != 0)
-assert(v8_enable_inspector)
 assert(!v8_enable_gdbjit)
 assert(!v8_imminent_deprecation_warnings)