Added Tab.SnapshotContent and MapsGL example to telemetry

tools/telemetry/telemetry/png_bitmap.py

Index: tools/telemetry/telemetry/png_bitmap.py
diff --git a/tools/telemetry/telemetry/png_bitmap.py b/tools/telemetry/telemetry/png_bitmap.py
new file mode 100644
index 0000000000000000000000000000000000000000..6914dfbbbaaad0b287e34cc2f8d6a09967466f17
--- /dev/null
+++ b/tools/telemetry/telemetry/png_bitmap.py
@@ -0,0 +1,69 @@
+# 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
+
+PNG_PATH = os.path.join(os.path.dirname(__file__), '../third_party/png')
+if PNG_PATH not in sys.path:
+  sys.path.append(PNG_PATH)
+
+import png # pylint: disable=F0401
+
+class PngColor(object):
+  """Encapsulates an RGB color retreived from a PngBitmap"""
+
+  def __init__(self, r, g, b, a=255):
+    self.r = r
+    self.g = g
+    self.b = b
+    self.a = a
+
+  def IsEqual(self, expected_color, tolerance=0):
+    """Verifies that the color is within a given tolerance of
+    the expected color"""
+    r_diff = abs(self.r - expected_color.r)
+    g_diff = abs(self.g - expected_color.g)
+    b_diff = abs(self.b - expected_color.b)
+    a_diff = abs(self.a - expected_color.a)
+    return (r_diff <= tolerance and g_diff <= tolerance
+        and b_diff <= tolerance and a_diff <= tolerance)
+
+  def AssertIsRGB(self, r, g, b, tolerance=0):
+    assert self.IsEqual(PngColor(r, g, b), tolerance)
+
+  def AssertIsRGBA(self, r, g, b, a, tolerance=0):
+    assert self.IsEqual(PngColor(r, g, b, a), tolerance)
+
+class PngBitmap(object):
+  """Utilities for parsing and inspecting inspecting a PNG"""
+
+  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 GetPixelColor(self, x, y):
+    """Returns a PngColor for the pixel at (x, y)"""
+    row = self._pixels[y]
+    offset = x * 4
+    return PngColor(row[offset], row[offset+1], row[offset+2], row[offset+3])
+
+  def WriteFile(self, path):
+    with open(path, "wb") as f:
+      f.write(self._png_data)