Disable flaky tests on Linux Release (AMD) GPU FYI

Disables several flaky tests which cause Linux Release (AMD) GPU FYI
to occasionally fail. These tests are not disabled on other bots, and each case has a
bug filed for it.

Disabled test cases:
ContextLost.WebGLContextLostFromGPUProcessExit
WebglConformance.conformance_textures_texture_size_cube_maps
WebglConformance.conformance_textures_texture_mips
WebglConformance.conformance_glsl_misc_shaders_with_invariance

BUG=479975,479983,479981,479952

Review URL: https://codereview.chromium.org/1099453004

Cr-Commit-Position: refs/heads/master@{#326670}

content/test/gpu/gpu_tests/context_lost_expectations.py

@@ -11,4 +11,7 @@ class ContextLostExpectations(GpuTestExpectations):
     # Sample Usage:
     # self.Fail('ContextLost.WebGLContextLostFromGPUProcessExit',
     #     ['mac', 'amd', ('nvidia', 0x1234)], bug=123)
-    pass
+
+    # AMD Radeon 6450
+    self.Fail('ContextLost.WebGLContextLostFromGPUProcessExit',
+        ['linux', ('amd', 0x6779)], bug=479975)

content/test/gpu/gpu_tests/webgl_conformance_expectations.py

@@ -198,6 +198,12 @@ class WebGLConformanceExpectations(GpuTestExpectations):
         ['linux', ('amd', 0x6779)], bug=436212)
     self.Fail('conformance/more/functions/uniformf.html',
         ['linux', ('amd', 0x6779)], bug=436212)
+    self.Fail('conformance/glsl/misc/shaders-with-invariance.html',
+        ['linux', ('amd', 0x6779)], bug=479952)
+    self.Fail('conformance/textures/texture-mips.html',
+        ['linux', ('amd', 0x6779)], bug=479981)
+    self.Fail('conformance/textures/texture-size-cube-maps.html',
+        ['linux', ('amd', 0x6779)], bug=479983)
 
     # Android failures
     self.Fail('deqp/data/gles2/shaders/constants.html',