Add --log-file=PATH switch to app_shell

Let users specify the logging location. The switch name is intentionally
left generic to allow other binaries to use the same flag.

Bug: 760431
Change-Id: I5f03f146b090fa5ba0e21718aeb27f5780981dde
Reviewed-on: https://chromium-review.googlesource.com/647314Reviewed-by: Nick Carter <nick@chromium.org>
Commit-Queue: Michael Giuffrida <michaelpg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#503645}

content/public/common/content_switches.cc

@@ -637,6 +637,11 @@ const char kLogGpuControlListDecisions[]    = "log-gpu-control-list-decisions";
 // INFO = 0, WARNING = 1, LOG_ERROR = 2, LOG_FATAL = 3.
 const char kLoggingLevel[]                  = "log-level";
 
+// Overrides the default file name to use for general-purpose logging (does not
+// affect which events are logged). Currently supported only in app_shell.
+// TODO(crbug.com/760431): Make this work in chrome and content_shell too.
+const char kLogFile[] = "log-file";
+
 // Enables saving net log events to a file and sets the file name to use.
 const char kLogNetLog[]                     = "log-net-log";
 

content/public/common/content_switches.h

@@ -189,6 +189,7 @@ CONTENT_EXPORT extern const char kJavaScriptFlags[];
 CONTENT_EXPORT extern const char kJavaScriptHarmony[];
 CONTENT_EXPORT extern const char kLogGpuControlListDecisions[];
 CONTENT_EXPORT extern const char kLoggingLevel[];
+CONTENT_EXPORT extern const char kLogFile[];
 CONTENT_EXPORT extern const char kLogNetLog[];
 CONTENT_EXPORT extern const char kMainFrameResizesAreOrientationChanges[];
 extern const char kMaxUntiledLayerHeight[];

extensions/shell/app/shell_main_delegate.cc

@@ -79,8 +79,13 @@ base::FilePath GetDataPath() {
 }
 
 void InitLogging() {
-  const base::FilePath log_path =
-      GetDataPath().Append(FILE_PATH_LITERAL("app_shell.log"));
+  base::FilePath log_path;
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(switches::kLogFile)) {
+    log_path = base::CommandLine::ForCurrentProcess()->GetSwitchValuePath(
+        switches::kLogFile);
+  } else {
+    log_path = GetDataPath().Append(FILE_PATH_LITERAL("app_shell.log"));
+  }
 
   // Set up log initialization settings.
   logging::LoggingSettings settings;