Added Tab.SnapshotContent and MapsGL example to telemetry

tools/telemetry/telemetry/snapshot.py

Index: tools/telemetry/telemetry/snapshot.py
diff --git a/tools/telemetry/telemetry/snapshot.py b/tools/telemetry/telemetry/snapshot.py
new file mode 100644
index 0000000000000000000000000000000000000000..e2a596a22b9a977b881d76dab5aa89ccc2b30396
--- /dev/null
+++ b/tools/telemetry/telemetry/snapshot.py
@@ -0,0 +1,50 @@
+# Copyright (c) 2012 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+import sys
+import os
+import base64
+
+sys.path.append(os.path.join(os.path.dirname(__file__), '../third_party'))
+import png # pylint: disable=F0401

[nduca, 2012/11/09 21:19:00]

this is a bit surprising, I dont like it. Is there a way to make this append
less global, e.g. third_party/png? you have third_party/png/png.py, right?

+

[nduca, 2012/11/09 21:19:00]

please also guard against this running twice, e.g. figure out the dir you plan
to append to sys.path. If its in the path, dont append it.

+class Snapshot(object):

[nduca, 2012/11/09 21:19:00]

Why call this snapshot and not, say, PngBitmap?

[nduca, 2012/11/09 21:19:00]

This class should be unit tested. Put a png in unittest_data, and have unit
tests that sanity check it

+  """Utilities for inspecting a snapshot of a tab"""
+
+  def __init__(self, base64_png):
+    self._png_data = base64.b64decode(base64_png)
+    self._png = png.Reader(bytes=self._png_data)
+    rgba8_data = self._png.asRGBA8()
+    self._width = rgba8_data[0]
+    self._height = rgba8_data[1]
+    self._pixels = list(rgba8_data[2])
+    self._metadata = rgba8_data[3]
+
+  @property
+  def width(self):
+    """Width of the snapshot"""
+    return self._width
+
+  @property
+  def height(self):
+    """Height of the snapshot"""
+    return self._height
+
+  def GetPixel(self, x, y):

[nduca, 2012/11/09 21:19:00]

GetPixelColor

+    """Returns a 3 element tuple describing the pixel color at (x, y)"""
+    row = self._pixels[y]
+    offset = x * 4
+    return [row[offset], row[offset + 1], row[offset + 2]]

[nduca, 2012/11/09 21:19:00]

make a color class

+
+  def CheckPixelColor(self, x, y, expected_color, tolerance=0):
+    """Verifies that the pixel at (x, y) is the expected color"""

[nduca, 2012/11/09 21:19:00]

This is a method on the color class.

+    pixel_color = self.GetPixel(x, y)
+    r_diff = abs(pixel_color[0] - expected_color[0])
+    g_diff = abs(pixel_color[1] - expected_color[1])
+    b_diff = abs(pixel_color[2] - expected_color[2])
+    return r_diff <= tolerance and g_diff <= tolerance and b_diff <= tolerance
+
+  def WriteFile(self, path):
+    f = open(path, "wb")

[nduca, 2012/11/09 21:19:00]

prefer this style
  with open(..) as f:
     f.write(..)

+    f.write(self._png_data)
+    f.close()