Telemetry: Add more details to inspector_backend exceptions.

Previously, inspector_backend would always throw a
DevtoolsTargetCrashException. Now, it throws either a
DevtoolsTargetCrashException or a TimeoutException. The CL also adds the
debugger_url to the exception as further debugging information.

There were exactly 2 files that tried to catch a DevtoolsTargetCrashException.
I changed fast_navigation_profile_extender to catch Error instead. I will be
improving this class in the future to have better exception handling.
chrome_proxy_measurements caught a DevtoolsTargetCrashException, but its
behavior is better suited by catching a TimeoutException.

BUG=460625

Review URL: https://codereview.chromium.org/959423003

Cr-Commit-Position: refs/heads/master@{#319193}

3 files changed, 46 insertions, 11 deletions

diff --git a/tools/chrome_proxy/integration_tests/chrome_proxy_measurements.py b/tools/chrome_proxy/integration_tests/chrome_proxy_measurements.py
index 0261b14..7fe40df 100644
--- a/tools/chrome_proxy/integration_tests/chrome_proxy_measurements.py
+++ b/tools/chrome_proxy/integration_tests/chrome_proxy_measurements.py
@@ -93,7 +93,7 @@ class ChromeProxyValidation(page_test.PageTest):
       if self._expect_timeout:
         raise metrics.ChromeProxyMetricException, (
             'Timeout was expected, but did not occur')
-    except exceptions.DevtoolsTargetCrashException, e:
+    except exceptions.TimeoutException as e:
       if self._expect_timeout:
         logging.warning('Navigation timeout on page %s',
                         page.name if page.name else page.url)
diff --git a/tools/perf/profile_creators/fast_navigation_profile_extender.py b/tools/perf/profile_creators/fast_navigation_profile_extender.py
index e490403..abcc8eb 100644
--- a/tools/perf/profile_creators/fast_navigation_profile_extender.py
+++ b/tools/perf/profile_creators/fast_navigation_profile_extender.py
@@ -161,7 +161,7 @@ class FastNavigationProfileExtender(object):
     """Retrives the URL of the tab."""
     try:
       return tab.EvaluateJavaScript('document.URL', timeout)
-    except (exceptions.DevtoolsTargetCrashException,
+    except (exceptions.Error,
         devtools_http.DevToolsClientConnectionError,
         devtools_http.DevToolsClientUrlError):
       return None
@@ -204,7 +204,7 @@ class FastNavigationProfileExtender(object):
 
       try:
         tab.Navigate(url, None, timeout_in_seconds)
-      except (exceptions.DevtoolsTargetCrashException,
+      except (exceptions.Error,
           devtools_http.DevToolsClientConnectionError,
           devtools_http.DevToolsClientUrlError):
         # We expect a time out. It's possible for other problems to arise, but
@@ -242,7 +242,7 @@ class FastNavigationProfileExtender(object):
       except exceptions.TimeoutException:
         # Ignore time outs.
         pass
-      except (exceptions.DevtoolsTargetCrashException,
+      except (exceptions.Error,
           devtools_http.DevToolsClientConnectionError,
           devtools_http.DevToolsClientUrlError):
         # If any error occurs, remove the tab. it's probably in an
diff --git a/tools/telemetry/telemetry/core/backends/chrome_inspector/inspector_backend.py b/tools/telemetry/telemetry/core/backends/chrome_inspector/inspector_backend.py
index 7361a38..886024e 100644
--- a/tools/telemetry/telemetry/core/backends/chrome_inspector/inspector_backend.py
+++ b/tools/telemetry/telemetry/core/backends/chrome_inspector/inspector_backend.py
@@ -198,17 +198,52 @@ class InspectorBackend(object):
       self._WaitForInspectorToGoAwayAndReconnect()
       return
     if res['method'] == 'Inspector.targetCrashed':
-      raise exceptions.DevtoolsTargetCrashException(self.app)
+      exception = exceptions.DevtoolsTargetCrashException(self.app)
+      self._AddDebuggingInformation(exception)
+      raise exception
 
   def _HandleError(self, error):
+    """Converts a websocket Exception into a Telemetry exception.
+
+    This method always raises a Telemetry exception. It appends debugging
+    information.
+
+    Args:
+      error: An instance of socket.error or websocket.WebSocketException.
+    Raises:
+      exception.TimeoutException: A timeout occured.
+      exception.DevtoolsTargetCrashException: On any other error, the most
+        likely explanation is that the devtool's target crashed.
+    """
+    if isinstance(error, websocket.WebSocketTimeoutException):
+      new_error = exceptions.TimeoutException()
+    else:
+      new_error = exceptions.DevtoolsTargetCrashException(self.app)
+
+    original_error_msg = 'Original exception:\n' + str(error)
+    new_error.AddDebuggingMessage(original_error_msg)
+    self._AddDebuggingInformation(new_error)
+
+    raise new_error
+
+  def _AddDebuggingInformation(self, error):
+    """Adds debugging information to error.
+
+    Args:
+      error: An instance of exceptions.Error.
+    """
     if self.IsInspectable():
-      raise exceptions.DevtoolsTargetCrashException(self.app,
+      msg = (
           'Received a socket error in the browser connection and the tab '
-          'still exists, assuming it timed out. '
-          'Error=%s' % error)
-    raise exceptions.DevtoolsTargetCrashException(self.app,
-        'Received a socket error in the browser connection and the tab no '
-        'longer exists, assuming it crashed. Error=%s' % error)
+          'still exists. The operation probably timed out.'
+      )
+    else:
+      msg = (
+          'Received a socket error in the browser connection and the tab no '
+          'longer exists. The tab probably crashed.'
+      )
+    error.AddDebuggingMessage(msg)
+    error.AddDebuggingMessage('Debugger url: %s' % self.debugger_url)
 
   def _WaitForInspectorToGoAwayAndReconnect(self):
     sys.stderr.write('The connection to Chrome was lost to the Inspector UI.\n')