AW: dump commandline state to logs for debugging

Similar to http://crrev/c/1266611, this dumps WebView's CommandLine
state (including the "--enable-features" and "--disable-features"
switches) to the log when the "dummy app"
("org.chromium.webview_log_verbosifier") is present.

Notably, this will give us an idea of whether the NetworkService is
enabled or not (FieldTrialList + CommandLine state + knowledge of
whether it is enabled-or-disabled-by-default should be sufficient).

This also adds a usage guide for the webview verbosifier app, including
the new commandline stuff.

Skipping presubmit for LOG(INFO).

NOPRESUBMIT=true

Bug: 929886, 918221
Test: Manual (following the steps in the new docs)
Test: Upload to gerrit > open file > click "gitiles"
Change-Id: I4c698d661c340f760e2a90da20439b44a56ea38b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1573087
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Reviewed-by: Richard Coles <torne@chromium.org>
Reviewed-by: Paul Miller <paulmiller@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652642}

android_webview/browser/aw_contents_statics.cc

@@ -13,6 +13,7 @@
 #include "base/android/scoped_java_ref.h"
 #include "base/bind.h"
 #include "base/callback.h"
+#include "base/command_line.h"
 #include "base/task/post_task.h"
 #include "components/google/core/common/google_util.h"
 #include "components/security_interstitials/core/urls.h"
@@ -133,6 +134,19 @@ void JNI_AwContentsStatics_SetCheckClearTextPermitted(
   AwURLRequestContextGetter::set_check_cleartext_permitted(permitted);
 }
 
+// static
+void JNI_AwContentsStatics_LogCommandLineForDebugging(JNIEnv* env) {
+  // Note: this should only be called for debugging purposes, since this is
+  // *very* spammy.
+  const base::CommandLine& command_line =
+      *base::CommandLine::ForCurrentProcess();
+  for (const auto& pair : command_line.GetSwitches()) {
+    const std::string& key = pair.first;
+    const base::CommandLine::StringType& value = pair.second;
+    LOG(INFO) << "WebViewCommandLine '" << key << "': '" << value << "'";
+  }
+}
+
 // static
 jboolean JNI_AwContentsStatics_IsMultiProcessEnabled(JNIEnv* env) {
   return !content::RenderProcessHost::run_renderer_in_process();

android_webview/glue/java/src/com/android/webview/chromium/WebViewChromiumAwInit.java

@@ -462,7 +462,14 @@ public class WebViewChromiumAwInit {
                 return;
             }
 
-            PostTask.postTask(UiThreadTaskTraits.DEFAULT, () -> FieldTrialList.logActiveTrials());
+            PostTask.postTask(UiThreadTaskTraits.BEST_EFFORT, () -> {
+                // TODO(ntfschr): CommandLine can change at any time. For simplicity, only log it
+                // once during startup.
+                AwContentsStatics.logCommandLineForDebugging();
+                // Field trials can be activated at any time. We'll continue logging them as they're
+                // activated.
+                FieldTrialList.logActiveTrials();
+            });
         });
     }
 

android_webview/java/src/org/chromium/android_webview/AwContentsStatics.java

@@ -123,6 +123,10 @@ public class AwContentsStatics {
         nativeSetCheckClearTextPermitted(permitted);
     }
 
+    public static void logCommandLineForDebugging() {
+        nativeLogCommandLineForDebugging();
+    }
+
     /**
      * Return the first substring consisting of the address of a physical location.
      * @see {@link android.webkit.WebView#findAddress(String)}
@@ -147,6 +151,7 @@ public class AwContentsStatics {
     //--------------------------------------------------------------------------------------------
     //  Native methods
     //--------------------------------------------------------------------------------------------
+    private static native void nativeLogCommandLineForDebugging();
     private static native String nativeGetSafeBrowsingPrivacyPolicyUrl();
     private static native void nativeClearClientCertPreferences(Runnable callback);
     private static native String nativeGetUnreachableWebDataUrl();

android_webview/tools/webview_log_verbosifier/README

-WebView Log Verbosifier is an empty dummy app. If this app is installed, WebView
-will log the active field trials, for debugging/QA purposes. A dummy app is used
-because it can be installed on any device, unlike command-line flags.

android_webview/tools/webview_log_verbosifier/README.md

+# WebView Log Verbosifier
+
+WebView Log Verbosifier is an empty dummy app (in fact, it cannot be launched).
+However, if this app is installed, WebView will log the active field trials and
+CommandLine flags, for debugging/QA purposes. A dummy app is used because it can
+be installed on any device (including user builds, where field trials are still
+relevant).
+
+## Build and install
+
+```shell
+autoninja -C out/Default webview_log_verbosifier_apk
+out/Default/bin/webview_log_verbosifier_apk install
+```
+
+## Searching logcat
+
+You can `grep` the logcat like so:
+
+```shell
+adb logcat | grep -i 'Active field trial' # Field trials, one per line
+adb logcat | grep -i 'WebViewCommandLine' # CommandLine switches, one per line
+adb logcat | grep -iE 'Active field trial|WebViewCommandLine' # Both
+```
+
+Then just start up any WebView app.
+
+## Uninstalling
+
+When you're done investigating flags/field trials, you can disable the logging
+by uninstalling the app:
+
+```shell
+out/Default/bin/webview_log_verbosifier_apk uninstall
+```