Add appengine/gcloud/mustache dependencies.

pkg/mustache/test/spec/comments.yml

+overview: |
+  Comment tags represent content that should never appear in the resulting
+  output.
+
+  The tag's content may contain any substring (including newlines) EXCEPT the
+  closing delimiter.
+
+  Comment tags SHOULD be treated as standalone when appropriate.
+tests:
+  - name: Inline
+    desc: Comment blocks should be removed from the template.
+    data: { }
+    template: '12345{{! Comment Block! }}67890'
+    expected: '1234567890'
+
+  - name: Multiline
+    desc: Multiline comments should be permitted.
+    data: { }
+    template: |
+      12345{{!
+        This is a
+        multi-line comment...
+      }}67890
+    expected: |
+      1234567890
+
+  - name: Standalone
+    desc: All standalone comment lines should be removed.
+    data: { }
+    template: |
+      Begin.
+      {{! Comment Block! }}
+      End.
+    expected: |
+      Begin.
+      End.
+
+  - name: Indented Standalone
+    desc: All standalone comment lines should be removed.
+    data: { }
+    template: |
+      Begin.
+        {{! Indented Comment Block! }}
+      End.
+    expected: |
+      Begin.
+      End.
+
+  - name: Standalone Line Endings
+    desc: '"\r\n" should be considered a newline for standalone tags.'
+    data: { }
+    template: "|\r\n{{! Standalone Comment }}\r\n|"
+    expected: "|\r\n|"
+
+  - name: Standalone Without Previous Line
+    desc: Standalone tags should not require a newline to precede them.
+    data: { }
+    template: "  {{! I'm Still Standalone }}\n!"
+    expected: "!"
+
+  - name: Standalone Without Newline
+    desc: Standalone tags should not require a newline to follow them.
+    data: { }
+    template: "!\n  {{! I'm Still Standalone }}"
+    expected: "!\n"
+
+  - name: Multiline Standalone
+    desc: All standalone comment lines should be removed.
+    data: { }
+    template: |
+      Begin.
+      {{!
+      Something's going on here...
+      }}
+      End.
+    expected: |
+      Begin.
+      End.
+
+  - name: Indented Multiline Standalone
+    desc: All standalone comment lines should be removed.
+    data: { }
+    template: |
+      Begin.
+        {{!
+          Something's going on here...
+        }}
+      End.
+    expected: |
+      Begin.
+      End.
+
+  - name: Indented Inline
+    desc: Inline comments should not strip whitespace
+    data: { }
+    template: "  12 {{! 34 }}\n"
+    expected: "  12 \n"
+
+  - name: Surrounding Whitespace
+    desc: Comment removal should preserve surrounding whitespace.
+    data: { }
+    template: '12345 {{! Comment Block! }} 67890'
+    expected: '12345  67890'